id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1306.4927 | Li-Ming Cao | Rong-Gen Cai and Li-Ming Cao | Generalized Formalism in Gauge-Invariant Gravitational Perturbations | review tex, 35 pages, no figure | Phys. Rev. D 88, 084047 (2013) | 10.1103/PhysRevD.88.084047 | ICTS-USTC-13-13 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By use of the gauge-invariant variables proposed by Kodama and Ishibashi, we
obtain the most general perturbation equations in the $(m+n)$-dimensional
spacetime with a warped product metric. These equations do not depend on the
spectral expansions of the Laplace-type operators on the $n$-dimensional
Einstein manifold. These equations enable us to have a complete gauge-invariant
perturbation theory and a well-defined spectral expansion for all modes and the
gauge invariance is kept for each mode. By studying perturbations of some
projections of Weyl tensor in the case of $m=2$, we define three Teukolsky-like
gauge-invariant variables and obtain the perturbation equations of these
variables by considering perturbations of the Penrose wave equations in the
$(2+n)$-dimensional Einstein spectime. In particular, we find the relations
between the Teukolsky-like gauge-invariant variables and the Kodama-Ishibashi
gauge-invariant variables. These relations imply that the Kodama-Ishibashi
gauge-invariant variables all come from the perturbations of Weyl tensor of the
spacetime.
| [
{
"created": "Thu, 20 Jun 2013 16:09:46 GMT",
"version": "v1"
}
] | 2013-11-13 | [
[
"Cai",
"Rong-Gen",
""
],
[
"Cao",
"Li-Ming",
""
]
] | By use of the gauge-invariant variables proposed by Kodama and Ishibashi, we obtain the most general perturbation equations in the $(m+n)$-dimensional spacetime with a warped product metric. These equations do not depend on the spectral expansions of the Laplace-type operators on the $n$-dimensional Einstein manifold. These equations enable us to have a complete gauge-invariant perturbation theory and a well-defined spectral expansion for all modes and the gauge invariance is kept for each mode. By studying perturbations of some projections of Weyl tensor in the case of $m=2$, we define three Teukolsky-like gauge-invariant variables and obtain the perturbation equations of these variables by considering perturbations of the Penrose wave equations in the $(2+n)$-dimensional Einstein spectime. In particular, we find the relations between the Teukolsky-like gauge-invariant variables and the Kodama-Ishibashi gauge-invariant variables. These relations imply that the Kodama-Ishibashi gauge-invariant variables all come from the perturbations of Weyl tensor of the spacetime. |
gr-qc/9907045 | Teviet Creighton | Teviet Creighton (California Institute of Technology) | Gravitational waves and the cosmological equation of state | 5 pages REVTeX, 3 figures | null | null | GRP-517 | gr-qc | null | Primordial gravitational waves are amplified during eras when their
wavelengths are pushed outside the cosmological horizon. This occurs in both
inflationary and ``pre-big-bang'' or ``bounce'' cosmologies. The spectrum is
expressed as a normalized energy density per unit logarithmic frequency,
denoted Omega. The spectral index (logarithmic slope) of Omega is simply
related to three properties of the early universe: (i) the gravitons' mean
initial quantum occupation number N(n) (=1/2 for a vacuum state), where n is
the (invariant) conformal frequency of the mode, and (ii) & (iii) the parameter
gamma=p/rho of the cosmological equation of state during the epoch when the
waves left the horizon (gamma=gamma_i) and when they reentered (gamma=gamma_f).
In the case of an inflationary cosmology, the spectral index is equal to
d(ln N)/d(ln n) + 2(gamma_i + 1)/(gamma_i + 1/3) + 2(gamma_f - 1/3)/(gamma_f
+ 1/3)
and for bounce cosmologies it is equal to
d(ln N)/d(ln n) + 4(gamma_i)/(gamma_i + 1/3) + 2(gamma_f - 1/3)/(gamma_f +
1/3)
These expressions are compared against various more model-specific results
given in the literature.
| [
{
"created": "Mon, 12 Jul 1999 21:00:54 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jul 1999 23:07:02 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Creighton",
"Teviet",
"",
"California Institute of Technology"
]
] | Primordial gravitational waves are amplified during eras when their wavelengths are pushed outside the cosmological horizon. This occurs in both inflationary and ``pre-big-bang'' or ``bounce'' cosmologies. The spectrum is expressed as a normalized energy density per unit logarithmic frequency, denoted Omega. The spectral index (logarithmic slope) of Omega is simply related to three properties of the early universe: (i) the gravitons' mean initial quantum occupation number N(n) (=1/2 for a vacuum state), where n is the (invariant) conformal frequency of the mode, and (ii) & (iii) the parameter gamma=p/rho of the cosmological equation of state during the epoch when the waves left the horizon (gamma=gamma_i) and when they reentered (gamma=gamma_f). In the case of an inflationary cosmology, the spectral index is equal to d(ln N)/d(ln n) + 2(gamma_i + 1)/(gamma_i + 1/3) + 2(gamma_f - 1/3)/(gamma_f + 1/3) and for bounce cosmologies it is equal to d(ln N)/d(ln n) + 4(gamma_i)/(gamma_i + 1/3) + 2(gamma_f - 1/3)/(gamma_f + 1/3) These expressions are compared against various more model-specific results given in the literature. |
1604.06051 | Peter Millington | Clare Burrage, Edmund J. Copeland, Peter Millington | Radiative Screening of Fifth Forces | 6 pages, 2 figures, revtex format; to match published version:
discussion of first-order thermal phase transitions included, additional
constraints taken into account and references expanded | Phys. Rev. Lett. 117, 211102 (2016) | 10.1103/PhysRevLett.117.211102 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a symmetron model in which the screening of fifth forces arises
at the one-loop level through the Coleman-Weinberg mechanism of spontaneous
symmetry breaking. We show that such a theory can avoid current constraints on
the existence of fifth forces but still has the potential to give rise to
observable deviations from general relativity, which could be seen in cold atom
experiments.
| [
{
"created": "Wed, 20 Apr 2016 18:21:12 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Nov 2016 18:05:52 GMT",
"version": "v2"
}
] | 2016-11-17 | [
[
"Burrage",
"Clare",
""
],
[
"Copeland",
"Edmund J.",
""
],
[
"Millington",
"Peter",
""
]
] | We describe a symmetron model in which the screening of fifth forces arises at the one-loop level through the Coleman-Weinberg mechanism of spontaneous symmetry breaking. We show that such a theory can avoid current constraints on the existence of fifth forces but still has the potential to give rise to observable deviations from general relativity, which could be seen in cold atom experiments. |
1707.01235 | Jie-Xiong Mo | Jie-Xiong Mo, Gu-Qiang Li | Holographic Heat engine within the framework of massive gravity | 9pages,4figures | null | 10.1007/JHEP05(2018)122 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Heat engine models are constructed within the framework of massive gravity in
this paper. For the four-dimensional charged black holes in massive gravity, it
is shown that the heat engines have a higher efficiency for the cases $m^2>0$
than for the case $m=0$ when $c_1<0, c_2<0$. Considering a specific example, we
show that the maximum efficiency can reach $0.9219$ while the efficiency for
$m=0$ reads $0.5014$. The existence of graviton mass improves the heat engine
efficiency significantly. The situation is more complicated for the
five-dimensional neutral black holes. Not only the $c_1, c_2, m^2$ exert
influence on the efficiency, but also the constant $c_3$ corresponding to the
third massive potential contributes to the efficiency. When $c_1<0, c_2<0,
c_3<0$, the heat engine efficiency of the cases $m^2>0$ is higher than that of
the case $m=0$. By studying the ratio $\eta/\eta_C$, we also probe how the
massive gravity influences the behavior of the heat engine efficiency
approaching the Carnot efficiency.
| [
{
"created": "Wed, 5 Jul 2017 07:11:56 GMT",
"version": "v1"
}
] | 2018-06-13 | [
[
"Mo",
"Jie-Xiong",
""
],
[
"Li",
"Gu-Qiang",
""
]
] | Heat engine models are constructed within the framework of massive gravity in this paper. For the four-dimensional charged black holes in massive gravity, it is shown that the heat engines have a higher efficiency for the cases $m^2>0$ than for the case $m=0$ when $c_1<0, c_2<0$. Considering a specific example, we show that the maximum efficiency can reach $0.9219$ while the efficiency for $m=0$ reads $0.5014$. The existence of graviton mass improves the heat engine efficiency significantly. The situation is more complicated for the five-dimensional neutral black holes. Not only the $c_1, c_2, m^2$ exert influence on the efficiency, but also the constant $c_3$ corresponding to the third massive potential contributes to the efficiency. When $c_1<0, c_2<0, c_3<0$, the heat engine efficiency of the cases $m^2>0$ is higher than that of the case $m=0$. By studying the ratio $\eta/\eta_C$, we also probe how the massive gravity influences the behavior of the heat engine efficiency approaching the Carnot efficiency. |
1312.1723 | Marco Astorino | Marco Astorino | Pair Creation of Rotating Black Holes | 13 pages, v2: typos corrected and reference added | Phys. Rev. D 89, 044022 (2014) | 10.1103/PhysRevD.89.044022 | CECS-PHY-13/10 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An exact and regular solution, describing a couple of charged and spinning
black holes, is generated in an external electromagnetic field, via Ernst
technique, in Einstein-Maxwell gravity. A wormhole instantonic solution
interpolating between the two black holes is constructed to discuss, at the
semi-classical level, the quantum process of creation rate, in an external
magnetic field, of this charged and spinning black hole pair.
| [
{
"created": "Thu, 5 Dec 2013 22:36:44 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Feb 2014 21:18:22 GMT",
"version": "v2"
}
] | 2014-02-28 | [
[
"Astorino",
"Marco",
""
]
] | An exact and regular solution, describing a couple of charged and spinning black holes, is generated in an external electromagnetic field, via Ernst technique, in Einstein-Maxwell gravity. A wormhole instantonic solution interpolating between the two black holes is constructed to discuss, at the semi-classical level, the quantum process of creation rate, in an external magnetic field, of this charged and spinning black hole pair. |
1905.13237 | Zachary Nasipak | Zachary Nasipak, Thomas Osburn, Charles R. Evans | Repeated faint quasinormal bursts in extreme-mass-ratio inspiral
waveforms: Evidence from frequency-domain scalar self-force calculations on
generic Kerr orbits | 28 pages, 11 figures, 5 tables; Updated to reflect published version | Phys. Rev. D 100, 064008 (2019) | 10.1103/PhysRevD.100.064008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We report development of a code to calculate the scalar self-force on a
scalar-charged particle moving on generic bound orbits in the Kerr spacetime.
The scalar self-force model allows rapid development of computational
techniques relevant to generic gravitational extreme-mass-ratio inspirals
(EMRIs). Our frequency-domain calculations are made with arbitrary numerical
precision code written in \textsc{Mathematica}. We extend spectral source
integration techniques to the Kerr spacetime, increasing computational
efficiency. We model orbits with nearly arbitrary inclinations
$0\leq\iota<\pi/2$ and eccentricities up to $e \lesssim 0.8$. This effort
extends earlier work by Warburton and Barack where motion was restricted to the
equatorial plane or to inclined spherical orbits. Consistent with a recent
discovery by Thornburg and Wardell \cite{ThorWard17} in time-domain
calculations, we observe self-force oscillations during the radially-outbound
portion of highly eccentric orbits around a rapidly rotating black hole. As
noted previously, these oscillations reflect coupling into the self-force by
quasinormal modes excited during pericenter passage. Our results confirm the
effect with a frequency-domain code. \emph{More importantly, we find that
quasinormal bursts (QNBs) appear directly in the waveform following each
periastron passage.} These faint bursts are shown to be a superposition of the
least-damped overtone (i.e., fundamental) of at least four ($l=m \le 4$)
quasinormal modes. Our results suggest that QNBs should appear in gravitational
waveforms, and thus provide a gauge-invariant signal. Potentially observable in
high signal-to-noise ratio EMRIs, QNBs would provide high-frequency components
to the parameter estimation problem that would complement low-frequency
elements of the waveform.
| [
{
"created": "Thu, 30 May 2019 18:00:17 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Sep 2019 16:42:29 GMT",
"version": "v2"
}
] | 2019-09-17 | [
[
"Nasipak",
"Zachary",
""
],
[
"Osburn",
"Thomas",
""
],
[
"Evans",
"Charles R.",
""
]
] | We report development of a code to calculate the scalar self-force on a scalar-charged particle moving on generic bound orbits in the Kerr spacetime. The scalar self-force model allows rapid development of computational techniques relevant to generic gravitational extreme-mass-ratio inspirals (EMRIs). Our frequency-domain calculations are made with arbitrary numerical precision code written in \textsc{Mathematica}. We extend spectral source integration techniques to the Kerr spacetime, increasing computational efficiency. We model orbits with nearly arbitrary inclinations $0\leq\iota<\pi/2$ and eccentricities up to $e \lesssim 0.8$. This effort extends earlier work by Warburton and Barack where motion was restricted to the equatorial plane or to inclined spherical orbits. Consistent with a recent discovery by Thornburg and Wardell \cite{ThorWard17} in time-domain calculations, we observe self-force oscillations during the radially-outbound portion of highly eccentric orbits around a rapidly rotating black hole. As noted previously, these oscillations reflect coupling into the self-force by quasinormal modes excited during pericenter passage. Our results confirm the effect with a frequency-domain code. \emph{More importantly, we find that quasinormal bursts (QNBs) appear directly in the waveform following each periastron passage.} These faint bursts are shown to be a superposition of the least-damped overtone (i.e., fundamental) of at least four ($l=m \le 4$) quasinormal modes. Our results suggest that QNBs should appear in gravitational waveforms, and thus provide a gauge-invariant signal. Potentially observable in high signal-to-noise ratio EMRIs, QNBs would provide high-frequency components to the parameter estimation problem that would complement low-frequency elements of the waveform. |
2201.08390 | Abhik Kumar Sanyal Dr. | Manas Chakrabortty, Kaushik Sarkar and Abhik Kumar Sanyal | The issue of Branched Hamiltonian in F(T) Teleparallel Gravity | 12 pages, 0 figures | International Journal of Modern Physics D, (2022) 2250083 (14
pages) (2022) | 10.1142/S0218271822500833 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As in the case of Lanczos-Lovelock gravity, the main advantage of F(T)
gravity is said to be that it leads to second order field equations, while F(R)
gravity theory leads to fourth order equations. We show that it is rather a
disadvantage, since it leads to the unresolved issue of `Branched Hamiltonian'.
The problem is bypassed in F(R,T) gravity theory.
| [
{
"created": "Thu, 20 Jan 2022 15:15:23 GMT",
"version": "v1"
},
{
"created": "Sat, 25 Jun 2022 03:29:35 GMT",
"version": "v2"
}
] | 2022-06-28 | [
[
"Chakrabortty",
"Manas",
""
],
[
"Sarkar",
"Kaushik",
""
],
[
"Sanyal",
"Abhik Kumar",
""
]
] | As in the case of Lanczos-Lovelock gravity, the main advantage of F(T) gravity is said to be that it leads to second order field equations, while F(R) gravity theory leads to fourth order equations. We show that it is rather a disadvantage, since it leads to the unresolved issue of `Branched Hamiltonian'. The problem is bypassed in F(R,T) gravity theory. |
1404.2236 | Matthew Williams Ph.D. | C.P. Burgess and M. Williams | Who You Gonna Call? Runaway Ghosts, Higher Derivatives and
Time-Dependence in EFTs | 12 pages | JHEP 1408 (2014) 074 | 10.1007/JHEP08(2014)074 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We briefly review the formulation of effective field theories (EFTs) in
time-dependent situations, with particular attention paid to their domain of
validity. Our main interest is the extent to which solutions of the EFT capture
the dynamics of the full theory. For a simple model we show by explicit
calculation that the low-energy action obtained from a sensible UV completion
need not take the restrictive form required to obtain only second-order field
equations, and we clarify why runaway solutions are nevertheless typically not
a problem for the EFT. Although our results will not be surprising to many, to
our knowledge they are only mentioned tangentially in the EFT literature, which
(with a few exceptions) largely addresses time-independent situations.
| [
{
"created": "Tue, 8 Apr 2014 17:56:43 GMT",
"version": "v1"
}
] | 2014-09-02 | [
[
"Burgess",
"C. P.",
""
],
[
"Williams",
"M.",
""
]
] | We briefly review the formulation of effective field theories (EFTs) in time-dependent situations, with particular attention paid to their domain of validity. Our main interest is the extent to which solutions of the EFT capture the dynamics of the full theory. For a simple model we show by explicit calculation that the low-energy action obtained from a sensible UV completion need not take the restrictive form required to obtain only second-order field equations, and we clarify why runaway solutions are nevertheless typically not a problem for the EFT. Although our results will not be surprising to many, to our knowledge they are only mentioned tangentially in the EFT literature, which (with a few exceptions) largely addresses time-independent situations. |
1211.0426 | Francisco Lobo | Francisco S. N. Lobo, Tiberiu Harko | Extended f(R,L_m) theories of gravity | 3 pages; contribution to the proceedings of the Thirteenth Marcel
Grossmann Meeting, Stockholm University, Sweden, 1-7 July, 2012 | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a maximal extension of the Hilbert-Einstein action and analyze
several interesting features of the theory. More specifically, the motion is
non-geodesic and takes place in the presence of an extra force. These models
could lead to some major differences, as compared to the predictions of General
Relativity or other modified theories of gravity, in several problems of
current interest, such as cosmology, gravitational collapse or the generation
of gravitational waves. Thus, the study of these phenomena may also provide
some specific signatures and effects, which could distinguish and discriminate
between the various gravitational models.
| [
{
"created": "Fri, 2 Nov 2012 11:42:03 GMT",
"version": "v1"
}
] | 2012-11-05 | [
[
"Lobo",
"Francisco S. N.",
""
],
[
"Harko",
"Tiberiu",
""
]
] | We consider a maximal extension of the Hilbert-Einstein action and analyze several interesting features of the theory. More specifically, the motion is non-geodesic and takes place in the presence of an extra force. These models could lead to some major differences, as compared to the predictions of General Relativity or other modified theories of gravity, in several problems of current interest, such as cosmology, gravitational collapse or the generation of gravitational waves. Thus, the study of these phenomena may also provide some specific signatures and effects, which could distinguish and discriminate between the various gravitational models. |
gr-qc/0402007 | Gilles Esposito-Farese | Gilles Esposito-Farese | Binary-pulsar tests of strong-field gravity and gravitational radiation
damping | 20 pages, LaTeX 2e, 7 postscript figures, contribution to 10th Marcel
Grossmann Meeting, 20-26 July 2003, Rio de Janeiro, Brazil | null | 10.1142/9789812704030_0039 | null | gr-qc astro-ph | null | This talk reviews the constraints imposed by binary-pulsar data on gravity
theories, focusing on ``tensor-scalar'' ones which are the best motivated
alternatives to general relativity. We recall that binary-pulsar tests are
qualitatively different from solar-system experiments, because of
nonperturbative strong-field effects which can occur in compact objects like
neutron stars, and because one can observe the effect of gravitational
radiation damping. Some theories which are strictly indistinguishable from
general relativity in the solar system are ruled out by binary-pulsar
observations. During the last months, several impressive new experimental data
have been published. Today, the most constraining binary pulsar is no longer
the celebrated (Hulse-Taylor) PSR B1913+16, but the neutron star-white dwarf
system PSR J1141-6545. In particular, in a region of the ``theory space'',
solar-system tests were known to give the tightest constraints; PSR J1141-6545
is now almost as powerful. We also comment on the possible scalar-field effects
for the detection of gravitational waves with future interferometers. The
presence of a scalar partner to the graviton might be detectable with the LISA
space experiment, but we already know that it would have a negligible effect
for LIGO and VIRGO, so that the general relativistic wave templates can be used
securely for these ground interferometers.
| [
{
"created": "Mon, 2 Feb 2004 13:53:33 GMT",
"version": "v1"
}
] | 2016-11-09 | [
[
"Esposito-Farese",
"Gilles",
""
]
] | This talk reviews the constraints imposed by binary-pulsar data on gravity theories, focusing on ``tensor-scalar'' ones which are the best motivated alternatives to general relativity. We recall that binary-pulsar tests are qualitatively different from solar-system experiments, because of nonperturbative strong-field effects which can occur in compact objects like neutron stars, and because one can observe the effect of gravitational radiation damping. Some theories which are strictly indistinguishable from general relativity in the solar system are ruled out by binary-pulsar observations. During the last months, several impressive new experimental data have been published. Today, the most constraining binary pulsar is no longer the celebrated (Hulse-Taylor) PSR B1913+16, but the neutron star-white dwarf system PSR J1141-6545. In particular, in a region of the ``theory space'', solar-system tests were known to give the tightest constraints; PSR J1141-6545 is now almost as powerful. We also comment on the possible scalar-field effects for the detection of gravitational waves with future interferometers. The presence of a scalar partner to the graviton might be detectable with the LISA space experiment, but we already know that it would have a negligible effect for LIGO and VIRGO, so that the general relativistic wave templates can be used securely for these ground interferometers. |
2303.13783 | Rikpratik Sengupta | Rikpratik Sengupta, Shounak Ghosh, B C Paul, Mehedi Kalam | Lorentzian wormholes in an emergent universe | 13 pages, 3 figures | Class. Quantum Grav. 40 (2023) 095009 | 10.1088/1361-6382/acc5d7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | A non-singular Emergent Universe (EU) scenario within the realm of standard
Relativistic physics requires a generalization of the Equation of State (EoS)
connecting the pressure and energy density. This generalized EoS is capable of
describing a composition of exotic matter, dark energy and cosmological dust
matter. Since the EU scenario is known to violate the Null Energy Condition, we
investigate the possibility of presence of static, spherically symmetric and
traversable Lorentzian wormholes in an EU. The obtained shape function is found
to satisfy the criteria for wormhole formation, besides the violation of the
NEC at the wormhole throat and ensuring traversability such that tidal forces
are within desirable limits. Also, the wormhole is found to be stable through
linear stability analysis. Most ${importantly}$, the numerical value of the
emergent universe parameter $B$ as estimated by our wormhole model is in
agreement with and lies within the range of values as constrained by
observational data in a cosmological context. Also, the negative sign of the
second EU parameter $A$ as obtained from our wormhole model is in agreement
with the one required for describing an EU, which further indicates on the
existence of such wormholes in an emergent universe ${without}$ accounting for
any additional exotic matter field or any modification to the gravitational
sector.
| [
{
"created": "Fri, 24 Mar 2023 03:49:54 GMT",
"version": "v1"
}
] | 2023-04-10 | [
[
"Sengupta",
"Rikpratik",
""
],
[
"Ghosh",
"Shounak",
""
],
[
"Paul",
"B C",
""
],
[
"Kalam",
"Mehedi",
""
]
] | A non-singular Emergent Universe (EU) scenario within the realm of standard Relativistic physics requires a generalization of the Equation of State (EoS) connecting the pressure and energy density. This generalized EoS is capable of describing a composition of exotic matter, dark energy and cosmological dust matter. Since the EU scenario is known to violate the Null Energy Condition, we investigate the possibility of presence of static, spherically symmetric and traversable Lorentzian wormholes in an EU. The obtained shape function is found to satisfy the criteria for wormhole formation, besides the violation of the NEC at the wormhole throat and ensuring traversability such that tidal forces are within desirable limits. Also, the wormhole is found to be stable through linear stability analysis. Most ${importantly}$, the numerical value of the emergent universe parameter $B$ as estimated by our wormhole model is in agreement with and lies within the range of values as constrained by observational data in a cosmological context. Also, the negative sign of the second EU parameter $A$ as obtained from our wormhole model is in agreement with the one required for describing an EU, which further indicates on the existence of such wormholes in an emergent universe ${without}$ accounting for any additional exotic matter field or any modification to the gravitational sector. |
gr-qc/0508022 | Farid Ya. Khalili | S.L.Danilishin, F.Ya.Khalili | To the practical design of the optical lever intracavity topology of
gravitational-wave detectors | 27 pages, 6 figures | Phys.Rev.D73:022002,2006 | 10.1103/PhysRevD.73.022002 | null | gr-qc | null | The QND intracavity topologies of gravitational-wave detectors proposed
several years ago allow, in principle, to obtain sensitivity significantly
better than the Standard Quantum Limit using relatively small anount of optical
pumping power. In this article we consider an improved more ``practical''
version of the optical lever intracavity scheme. It differs from the original
version by the symmetry which allows to suppress influence of the input light
amplitude fluctuation. In addition, it provides the means to inject optical
pumping inside the scheme without increase of optical losses.
We consider also sensitivity limitations imposed by the local meter which is
the key element of the intracavity topologies. Two variants of the local meter
are analyzed, which are based on the spectral variation measurement and on the
Discrete Sampling Variation Measurement, correspondingly. The former one, while
can not be considered as a candidate for a practical implementation, allows, in
principle, to obtain the best sensitivity and thus can be considered as an
ideal ``asymptotic case'' for all other schemes. The DSVM-based local meter can
be considered as a realistic scheme but its sensitivity, unfortunately, is by
far not so good just due to a couple of peculiar numeric factors specific for
this scheme.
From our point of view search of new methods of mechanical QND measurements
probably based on improved DSVM scheme or which combine the local meter with
the pondermotive squeezing technique, is necessary.
| [
{
"created": "Fri, 5 Aug 2005 12:28:44 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Danilishin",
"S. L.",
""
],
[
"Khalili",
"F. Ya.",
""
]
] | The QND intracavity topologies of gravitational-wave detectors proposed several years ago allow, in principle, to obtain sensitivity significantly better than the Standard Quantum Limit using relatively small anount of optical pumping power. In this article we consider an improved more ``practical'' version of the optical lever intracavity scheme. It differs from the original version by the symmetry which allows to suppress influence of the input light amplitude fluctuation. In addition, it provides the means to inject optical pumping inside the scheme without increase of optical losses. We consider also sensitivity limitations imposed by the local meter which is the key element of the intracavity topologies. Two variants of the local meter are analyzed, which are based on the spectral variation measurement and on the Discrete Sampling Variation Measurement, correspondingly. The former one, while can not be considered as a candidate for a practical implementation, allows, in principle, to obtain the best sensitivity and thus can be considered as an ideal ``asymptotic case'' for all other schemes. The DSVM-based local meter can be considered as a realistic scheme but its sensitivity, unfortunately, is by far not so good just due to a couple of peculiar numeric factors specific for this scheme. From our point of view search of new methods of mechanical QND measurements probably based on improved DSVM scheme or which combine the local meter with the pondermotive squeezing technique, is necessary. |
1604.04748 | Iver Brevik | I. Brevik, V. V. Obukhov, and A. V. Timoshkin | Inflationary Cosmology Leading to a Soft Type Singularity | 7 pages, no figures, to appear in Mod. Phys. Lett. A. One reference
added | Mod. Phys. Lett. A, Vol 13, No. 18 (2016) 1650105 | 10.1142/S0217732316501054 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A remarkable property of modern cosmology is that it allows for a special
case of symmetry, consisting in the possibility of describing the early-time
acceleration (inflation) and the late-time acceleration using the same
theoretical framework. In this paper we consider various cosmological models
corresponding to a generalized form for the equation of state for the fluid in
a flat Friedmann -Robertson-Walker universe, emphasizing cases where the
so-called type IV singular inflation is encountered in the future. This is a
soft (non-crushing) kind of singularity. Parameter values for an inhomogeneous
equation of state leading to singular inflation are obtained. We present models
for which there are two type IV singularities, the first corresponding to the
end of the inflationary era and the second to a late time event. We also study
the correspondence between the theoretical slow-roll parameters leading to type
IV singular inflation and the recent results observed by the Planck satellite.
| [
{
"created": "Sat, 16 Apr 2016 13:44:35 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Apr 2016 14:17:31 GMT",
"version": "v2"
}
] | 2016-06-14 | [
[
"Brevik",
"I.",
""
],
[
"Obukhov",
"V. V.",
""
],
[
"Timoshkin",
"A. V.",
""
]
] | A remarkable property of modern cosmology is that it allows for a special case of symmetry, consisting in the possibility of describing the early-time acceleration (inflation) and the late-time acceleration using the same theoretical framework. In this paper we consider various cosmological models corresponding to a generalized form for the equation of state for the fluid in a flat Friedmann -Robertson-Walker universe, emphasizing cases where the so-called type IV singular inflation is encountered in the future. This is a soft (non-crushing) kind of singularity. Parameter values for an inhomogeneous equation of state leading to singular inflation are obtained. We present models for which there are two type IV singularities, the first corresponding to the end of the inflationary era and the second to a late time event. We also study the correspondence between the theoretical slow-roll parameters leading to type IV singular inflation and the recent results observed by the Planck satellite. |
0912.3517 | Enrico Barausse | Enrico Barausse and Alessandra Buonanno (Univ. of Maryland) | An improved effective-one-body Hamiltonian for spinning black-hole
binaries | 22 pages, 9 figures. Minor changes to match version accepted for
publication in PRD | Phys.Rev.D81:084024,2010 | 10.1103/PhysRevD.81.084024 | null | gr-qc astro-ph.CO astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Building on a recent paper in which we computed the canonical Hamiltonian of
a spinning test particle in curved spacetime, at linear order in the particle's
spin, we work out an improved effective-one-body (EOB) Hamiltonian for spinning
black-hole binaries. As in previous descriptions, we endow the effective
particle not only with a mass m, but also with a spin S*. Thus, the effective
particle interacts with the effective Kerr background (having spin S_Kerr)
through a geodesic-type interaction and an additional spin-dependent
interaction proportional to S*. When expanded in post-Newtonian (PN) orders,
the EOB Hamiltonian reproduces the leading order spin-spin coupling and the
spin-orbit coupling through 2.5PN order, for any mass-ratio. Also, it
reproduces all spin-orbit couplings in the test-particle limit. Similarly to
the test-particle limit case, when we restrict the EOB dynamics to spins
aligned or antialigned with the orbital angular momentum, for which circular
orbits exist, the EOB dynamics has several interesting features, such as the
existence of an innermost stable circular orbit, a photon circular orbit, and a
maximum in the orbital frequency during the plunge subsequent to the inspiral.
These properties are crucial for reproducing the dynamics and
gravitational-wave emission of spinning black-hole binaries, as calculated in
numerical relativity simulations.
| [
{
"created": "Thu, 17 Dec 2009 20:56:28 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Feb 2010 20:25:08 GMT",
"version": "v2"
}
] | 2010-05-12 | [
[
"Barausse",
"Enrico",
"",
"Univ. of Maryland"
],
[
"Buonanno",
"Alessandra",
"",
"Univ. of Maryland"
]
] | Building on a recent paper in which we computed the canonical Hamiltonian of a spinning test particle in curved spacetime, at linear order in the particle's spin, we work out an improved effective-one-body (EOB) Hamiltonian for spinning black-hole binaries. As in previous descriptions, we endow the effective particle not only with a mass m, but also with a spin S*. Thus, the effective particle interacts with the effective Kerr background (having spin S_Kerr) through a geodesic-type interaction and an additional spin-dependent interaction proportional to S*. When expanded in post-Newtonian (PN) orders, the EOB Hamiltonian reproduces the leading order spin-spin coupling and the spin-orbit coupling through 2.5PN order, for any mass-ratio. Also, it reproduces all spin-orbit couplings in the test-particle limit. Similarly to the test-particle limit case, when we restrict the EOB dynamics to spins aligned or antialigned with the orbital angular momentum, for which circular orbits exist, the EOB dynamics has several interesting features, such as the existence of an innermost stable circular orbit, a photon circular orbit, and a maximum in the orbital frequency during the plunge subsequent to the inspiral. These properties are crucial for reproducing the dynamics and gravitational-wave emission of spinning black-hole binaries, as calculated in numerical relativity simulations. |
1203.6869 | Torsten Sch\"onfeld | Catherine Meusburger and Torsten Sch\"onfeld | Gauge fixing in (2+1)-gravity with vanishing cosmological constant | Talk given at the Workshop on Noncommutative Field Theory and Gravity
Corfu, September 7 - 11, 2011; 20 pages, 6 figures | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply Dirac's gauge fixing procedure to (2+1)-gravity with vanishing
cosmological constant. For general gauge fixing conditions based on two point
particles, this yields explicit expressions for the Dirac bracket. We explain
how gauge fixing is related to the introduction of an observer into the theory
and show that the Dirac bracket is determined by a classical dynamical
r-matrix. Its two dynamical variables correspond to the mass and spin of a cone
that describes the residual degrees of freedom of the spacetime. We show that
different gauge fixing conditions and different choices of observers are
related by dynamical Poincar\'e transformations. This allows us to locally
classify all Dirac brackets resulting from the gauge fixing and to relate them
to a set of particularly simple solutions associated with the centre-of-mass
frame of the spacetime.
| [
{
"created": "Fri, 30 Mar 2012 17:45:18 GMT",
"version": "v1"
},
{
"created": "Thu, 31 May 2012 12:03:10 GMT",
"version": "v2"
}
] | 2012-06-01 | [
[
"Meusburger",
"Catherine",
""
],
[
"Schönfeld",
"Torsten",
""
]
] | We apply Dirac's gauge fixing procedure to (2+1)-gravity with vanishing cosmological constant. For general gauge fixing conditions based on two point particles, this yields explicit expressions for the Dirac bracket. We explain how gauge fixing is related to the introduction of an observer into the theory and show that the Dirac bracket is determined by a classical dynamical r-matrix. Its two dynamical variables correspond to the mass and spin of a cone that describes the residual degrees of freedom of the spacetime. We show that different gauge fixing conditions and different choices of observers are related by dynamical Poincar\'e transformations. This allows us to locally classify all Dirac brackets resulting from the gauge fixing and to relate them to a set of particularly simple solutions associated with the centre-of-mass frame of the spacetime. |
2202.04253 | Yuki Kawasaki | Yuki Kawasaki, Ryuma Shimizu, Tomohiro Ishikawa, Koji Nagano, Shoki
Iwaguchi, Izyumi Watanabe, Wu Bin, Shuichiro Yokoyama, and Seiji Kawamura | Optimization of Design Parameters for Gravitational Wave Detector DECIGO
Including Fundamental Noises | 16 pages, 8 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The DECi hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a
space gravitational wave (GW) detector. DECIGO was originally designed to be
sensitive enough to observe primordial GW background (PGW). However, due to the
lowered upper limit of the PGW by the Planck observation, further improvement
of the target sensitivity of DECIGO is required. In the previous studies,
DECIGO's parameters were optimized to maximize the signal-to-noise ratio (SNR)
of the PGW to quantum noise including the effect of diffraction loss. To
simulate the SNR more realistically, we optimize DECIGO's parameters
considering the GWs from double white dwarfs (DWDs) and the thermal noise of
test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In
addition, we consider two kinds of thermal noise: thermal noise in a residual
gas and internal thermal noise. To investigate how the mirror geometry affects
the sensitivity, we calculate it by changing the mirror mass, keeping the
mirror thickness, and vice versa. As a result, we obtained the optimums for the
parameters that maximize the SNR that depends on the mirror radius. This result
shows that a thick mirror with a large radius gives a good SNR and enables us
to optimize the design of DECIGO based on the feasibility study of the mirror
size in the future.
| [
{
"created": "Wed, 9 Feb 2022 03:17:37 GMT",
"version": "v1"
}
] | 2022-02-10 | [
[
"Kawasaki",
"Yuki",
""
],
[
"Shimizu",
"Ryuma",
""
],
[
"Ishikawa",
"Tomohiro",
""
],
[
"Nagano",
"Koji",
""
],
[
"Iwaguchi",
"Shoki",
""
],
[
"Watanabe",
"Izyumi",
""
],
[
"Bin",
"Wu",
""
],
[
"Yokoyama",
"Shuichiro",
""
],
[
"Kawamura",
"Seiji",
""
]
] | The DECi hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies, DECIGO's parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW to quantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we optimize DECIGO's parameters considering the GWs from double white dwarfs (DWDs) and the thermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it by changing the mirror mass, keeping the mirror thickness, and vice versa. As a result, we obtained the optimums for the parameters that maximize the SNR that depends on the mirror radius. This result shows that a thick mirror with a large radius gives a good SNR and enables us to optimize the design of DECIGO based on the feasibility study of the mirror size in the future. |
2207.05066 | Yurii Ignat'ev | Yu. G. Ignat'ev | Single-field model of gravitational-scalar instability. I. Evolution of
perturbations | 18 pages, 23 figures, 16 references | Gravit. Cosmol. 28 (2022) 275-290 | 10.1134/S0202289322030045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | On the basis of the previously formulated mathematical model of a statistical
system with a scalar interaction of fermions and the theory of
gravitational-scalar instability of a cosmological model based on a
two-component statistical system of scalarly charged degenerate fermions, a
numerical model of the cosmological evolution of gravitational-scalar
perturbations for a one-component cosmological system with a canonical scalar
interaction is constructed and studied. The influence of the magnitude of the
scalar charge of fermions on the differential and integral parameters of the
instability is revealed. It is shown that the gravitational-scalar instability
in the early stages of expansion in the model under study arises at
sufficiently small scalar charges. 4 fundamentally different types of
perturbations are identified, as well as 4 types of gravitational-scalar
instability, determined by the fundamental parameters of the model. Examples of
numerical models are given that provide large values of the increments of the
increase in the amplitude of perturbations.
| [
{
"created": "Sun, 10 Jul 2022 11:22:24 GMT",
"version": "v1"
}
] | 2022-07-13 | [
[
"Ignat'ev",
"Yu. G.",
""
]
] | On the basis of the previously formulated mathematical model of a statistical system with a scalar interaction of fermions and the theory of gravitational-scalar instability of a cosmological model based on a two-component statistical system of scalarly charged degenerate fermions, a numerical model of the cosmological evolution of gravitational-scalar perturbations for a one-component cosmological system with a canonical scalar interaction is constructed and studied. The influence of the magnitude of the scalar charge of fermions on the differential and integral parameters of the instability is revealed. It is shown that the gravitational-scalar instability in the early stages of expansion in the model under study arises at sufficiently small scalar charges. 4 fundamentally different types of perturbations are identified, as well as 4 types of gravitational-scalar instability, determined by the fundamental parameters of the model. Examples of numerical models are given that provide large values of the increments of the increase in the amplitude of perturbations. |
1409.7872 | Sunil Maharaj | Apratim Ganguly, Sushant G. Ghosh and Sunil D. Maharaj | Accretion onto a black hole in a string cloud background | 9 pages, To appear in Phys. Rev. D | Phys. Rev. D 90, 064037 (2014) | 10.1103/PhysRevD.90.064037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the accretion process onto the black hole with a string cloud
background, where the horizon of the black hole has an enlarged radius $r_H=2
M/(1-\alpha)$, due to the string cloud parameter $\alpha\; (0 \leq \alpha <
1)$. The problem of stationary, spherically symmetric accretion of a polytropic
fluid is analysed to obtain an analytic solution for such a perturbation.
Generalised expressions for the accretion rate $\dot{M}$, critical radius
$r_s$, and other flow parameters are found. The accretion rate $\dot{M}$ is an
explicit function of the black hole mass $M$, as well as the gas boundary
conditions and the string cloud parameter $\alpha$. We also find the gas
compression ratios and temperature profiles below the accretion radius and at
the event horizon. It is shown that the mass accretion rate, for both the
relativistic and the non-relativistic fluid by a black hole in the string cloud
model, increases with increase in $\alpha$.
| [
{
"created": "Sun, 28 Sep 2014 07:18:50 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Ganguly",
"Apratim",
""
],
[
"Ghosh",
"Sushant G.",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | We examine the accretion process onto the black hole with a string cloud background, where the horizon of the black hole has an enlarged radius $r_H=2 M/(1-\alpha)$, due to the string cloud parameter $\alpha\; (0 \leq \alpha < 1)$. The problem of stationary, spherically symmetric accretion of a polytropic fluid is analysed to obtain an analytic solution for such a perturbation. Generalised expressions for the accretion rate $\dot{M}$, critical radius $r_s$, and other flow parameters are found. The accretion rate $\dot{M}$ is an explicit function of the black hole mass $M$, as well as the gas boundary conditions and the string cloud parameter $\alpha$. We also find the gas compression ratios and temperature profiles below the accretion radius and at the event horizon. It is shown that the mass accretion rate, for both the relativistic and the non-relativistic fluid by a black hole in the string cloud model, increases with increase in $\alpha$. |
0807.2055 | Alberto Rozas-Fernandez | Pedro F. Gonz\'alez-D\'iaz and Alberto Rozas-Fern\'andez | Quantum cosmic models and thermodynamics | 15 pages, 1 figure, accepted for publication in Class. Quantum Grav | Class.Quant.Grav.25:175023,2008 | 10.1088/0264-9381/25/17/175023 | IFF-RCA-08-02 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The current accelerating phase of the evolution of the universe is considered
by constructing most economical cosmic models that use just general relativity
and some dominating quantum effects associated with the probabilistic
description of quantum physics. Two of such models are explicitly analyzed.
They are based on the existence of a sub-quantum potential and correspond to a
generalization of the spatially flat exponential model of de Sitter space. The
thermodynamics of these two cosmic solutions is discussed, using the second
principle as a guide to choose which among the two is more feasible. The paper
also discusses the relativistic physics on which the models are based, their
holographic description, some implications from the classical energy
conditions, and an interpretation of dark energy in terms of the entangled
energy of the universe.
| [
{
"created": "Sun, 13 Jul 2008 19:02:30 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"González-Díaz",
"Pedro F.",
""
],
[
"Rozas-Fernández",
"Alberto",
""
]
] | The current accelerating phase of the evolution of the universe is considered by constructing most economical cosmic models that use just general relativity and some dominating quantum effects associated with the probabilistic description of quantum physics. Two of such models are explicitly analyzed. They are based on the existence of a sub-quantum potential and correspond to a generalization of the spatially flat exponential model of de Sitter space. The thermodynamics of these two cosmic solutions is discussed, using the second principle as a guide to choose which among the two is more feasible. The paper also discusses the relativistic physics on which the models are based, their holographic description, some implications from the classical energy conditions, and an interpretation of dark energy in terms of the entangled energy of the universe. |
2301.13213 | Takuya Takahashi | Takuya Takahashi, Hidetoshi Omiya, Takahiro Tanaka | Evolution of binary systems accompanying axion clouds in extreme mass
ratio inspirals | 15 pages, 13 figures, 1 table | null | 10.1103/PhysRevD.107.103020 | null | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | Superradiant instability of rotating black holes (BHs) leads to the formation
of a cloud of ultralight bosons, such as axions. When the BH with the cloud
belongs to a binary system and is in an inspiraling orbit, the resonant
transition between the axion's bound states can occur. We study the history of
the evolution of the binary system accompanying the cloud composed of the
fastest growing mode, and its impact on the observational signatures,
especially for small mass ratio cases. In this case, the hyperfine resonance,
which has a very small resonance frequency, is relevant. Therefore, due to the
long timescale, we should take into account the decaying process of axions in
the transition destination mode, the backreaction to the orbital motion and the
central BH, and gravitational emission from the cloud. We present a formulation
to examine the evolution of the system around the resonance and useful
expressions for the analysis. As a result, we found the mass of the cloud that
can remain after the resonance is, at most, about $10^{-5}$ of the central BH.
The maximum remaining cloud mass is achieved when the mass ratio of the binary
is $q\sim10^{-3}$. In addition, we show that the resonant transition hardly
changes the BH mass and spin distribution, while the associated modification of
the gravitational wave frequency evolution when the binary pass through the
resonance can be a signature of the presence of the cloud.
| [
{
"created": "Mon, 30 Jan 2023 19:00:02 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Feb 2023 13:38:06 GMT",
"version": "v2"
}
] | 2023-05-24 | [
[
"Takahashi",
"Takuya",
""
],
[
"Omiya",
"Hidetoshi",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | Superradiant instability of rotating black holes (BHs) leads to the formation of a cloud of ultralight bosons, such as axions. When the BH with the cloud belongs to a binary system and is in an inspiraling orbit, the resonant transition between the axion's bound states can occur. We study the history of the evolution of the binary system accompanying the cloud composed of the fastest growing mode, and its impact on the observational signatures, especially for small mass ratio cases. In this case, the hyperfine resonance, which has a very small resonance frequency, is relevant. Therefore, due to the long timescale, we should take into account the decaying process of axions in the transition destination mode, the backreaction to the orbital motion and the central BH, and gravitational emission from the cloud. We present a formulation to examine the evolution of the system around the resonance and useful expressions for the analysis. As a result, we found the mass of the cloud that can remain after the resonance is, at most, about $10^{-5}$ of the central BH. The maximum remaining cloud mass is achieved when the mass ratio of the binary is $q\sim10^{-3}$. In addition, we show that the resonant transition hardly changes the BH mass and spin distribution, while the associated modification of the gravitational wave frequency evolution when the binary pass through the resonance can be a signature of the presence of the cloud. |
gr-qc/9806085 | Dr. Panagiota Kanti | P. Kanti, J. Rizos and K. Tamvakis | Singularity-free cosmological solutions in quadratic gravity | Latex, 25 pages, 6 figures, some explanatory sentences and Comments
added, version to appear in Physical Review D | Phys. Rev. D 59, 083512 (1999) | 10.1103/PhysRevD.59.083512 | null | gr-qc hep-ph hep-th | null | We study a general field theory of a scalar field coupled to gravity through
a quadratic Gauss-Bonnet term $\xi(\phi) R^2_{GB}$. The coupling function has
the form $\xi(\phi)=\phi^n$, where $n$ is a positive integer. In the absence of
the Gauss-Bonnet term, the cosmological solutions for an empty universe and a
universe dominated by the energy-momentum tensor of a scalar field are always
characterized by the occurrence of a true cosmological singularity. By
employing analytical and numerical methods, we show that, in the presence of
the quadratic Gauss-Bonnet term, for the dual case of even $n$, the set of
solutions of the classical equations of motion in a curved FRW background
includes singularity-free cosmological solutions. The singular solutions are
shown to be confined in a part of the phase space of the theory allowing the
non-singular solutions to fill the rest of the space. We conjecture that the
same theory with a general coupling function that satisfies certain criteria
may lead to non-singular cosmological solutions.
| [
{
"created": "Sun, 21 Jun 1998 09:37:00 GMT",
"version": "v1"
},
{
"created": "Sun, 22 Nov 1998 14:09:34 GMT",
"version": "v2"
}
] | 2016-08-25 | [
[
"Kanti",
"P.",
""
],
[
"Rizos",
"J.",
""
],
[
"Tamvakis",
"K.",
""
]
] | We study a general field theory of a scalar field coupled to gravity through a quadratic Gauss-Bonnet term $\xi(\phi) R^2_{GB}$. The coupling function has the form $\xi(\phi)=\phi^n$, where $n$ is a positive integer. In the absence of the Gauss-Bonnet term, the cosmological solutions for an empty universe and a universe dominated by the energy-momentum tensor of a scalar field are always characterized by the occurrence of a true cosmological singularity. By employing analytical and numerical methods, we show that, in the presence of the quadratic Gauss-Bonnet term, for the dual case of even $n$, the set of solutions of the classical equations of motion in a curved FRW background includes singularity-free cosmological solutions. The singular solutions are shown to be confined in a part of the phase space of the theory allowing the non-singular solutions to fill the rest of the space. We conjecture that the same theory with a general coupling function that satisfies certain criteria may lead to non-singular cosmological solutions. |
2308.10742 | Askar Ali | Askar Ali, Ali \"Ovg\"un | Topological dyonic black holes of massive gravity with generalized
quasitopological electromagnetism | 24 pages and 15 figures | Eur. Phys. J. C (2024) 84:378 | 10.1140/epjc/s10052-024-12710-z | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper we investigate new dyonic black holes of massive gravity
sourced by generalized quasitopological electromagnetism in arbitrary
dimensions. We begin by deriving the exact solution to the field equations
defining these black holes and look at how graviton's mass, dimensionality
parameter, and quasitopological electromagnetic field affect the horizon
structure of anti-de Sitter dyonic black holes. We also explore the asymptotic
behaviour of the curvature invariants at both the origin and infinity to
analyze the geometric structure of the resultant black holes. We also compute
the conserved and thermodynamic quantities of these dyonic black holes with the
help of established techniques and known formulas. After investigating the
relevancy of first law, we look at how various parameters influence the local
thermodynamic stability of resultant black hole solution. We also examine how
thermal fluctuations affect the local stability of dyonic black holes in
massive gravity. Finally, we study the shadow cast of the black hole.
| [
{
"created": "Mon, 21 Aug 2023 14:15:20 GMT",
"version": "v1"
}
] | 2024-06-11 | [
[
"Ali",
"Askar",
""
],
[
"Övgün",
"Ali",
""
]
] | In this paper we investigate new dyonic black holes of massive gravity sourced by generalized quasitopological electromagnetism in arbitrary dimensions. We begin by deriving the exact solution to the field equations defining these black holes and look at how graviton's mass, dimensionality parameter, and quasitopological electromagnetic field affect the horizon structure of anti-de Sitter dyonic black holes. We also explore the asymptotic behaviour of the curvature invariants at both the origin and infinity to analyze the geometric structure of the resultant black holes. We also compute the conserved and thermodynamic quantities of these dyonic black holes with the help of established techniques and known formulas. After investigating the relevancy of first law, we look at how various parameters influence the local thermodynamic stability of resultant black hole solution. We also examine how thermal fluctuations affect the local stability of dyonic black holes in massive gravity. Finally, we study the shadow cast of the black hole. |
gr-qc/0011010 | Mariano Cadoni | M. Cadoni, P. G. L. Mana | Hamiltonians for a general dilaton gravity theory on a spacetime with a
non-orthogonal, timelike or spacelike outer boundary | 17 pages, 3 figures. Typos corrected | Class.Quant.Grav. 18 (2001) 779-792 | 10.1088/0264-9381/18/5/302 | INFNCA-TH0020 | gr-qc | null | A generalization of two recently proposed general relativity Hamiltonians, to
the case of a general (d+1)-dimensional dilaton gravity theory in a manifold
with a timelike or spacelike outer boundary, is presented.
| [
{
"created": "Fri, 3 Nov 2000 21:00:58 GMT",
"version": "v1"
},
{
"created": "Sun, 5 Nov 2000 12:48:18 GMT",
"version": "v2"
},
{
"created": "Fri, 12 Jan 2001 17:09:53 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Cadoni",
"M.",
""
],
[
"Mana",
"P. G. L.",
""
]
] | A generalization of two recently proposed general relativity Hamiltonians, to the case of a general (d+1)-dimensional dilaton gravity theory in a manifold with a timelike or spacelike outer boundary, is presented. |
1210.4108 | Christian Pfeifer | Mattias N. R. Wohlfarth, Christian Pfeifer | Local spacetime effects on gyroscope systems | 19 pages, 2 figures, journal references added | Phys. Rev. D 87, 024031 (2013) | 10.1103/PhysRevD.87.024031 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We give a precise theoretical description of initially aligned sets of
orthogonal gyroscopes which are transported along different paths from some
initial point to the same final point in spacetime. These gyroscope systems can
be used to synchronize separated observers' spatial frames by free fall along
timelike geodesics. We find that initially aligned gyroscope systems, or
spatial frames, lose their synchronization due to the curvature of spacetime
and their relative motion. On the basis of our results we propose a simple
experiment which enables observers to determine locally whether their spacetime
is described by a rotating Kerr or a non-rotating Schwarzschild metric.
| [
{
"created": "Mon, 15 Oct 2012 17:10:53 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Jan 2013 09:02:00 GMT",
"version": "v2"
}
] | 2013-01-30 | [
[
"Wohlfarth",
"Mattias N. R.",
""
],
[
"Pfeifer",
"Christian",
""
]
] | We give a precise theoretical description of initially aligned sets of orthogonal gyroscopes which are transported along different paths from some initial point to the same final point in spacetime. These gyroscope systems can be used to synchronize separated observers' spatial frames by free fall along timelike geodesics. We find that initially aligned gyroscope systems, or spatial frames, lose their synchronization due to the curvature of spacetime and their relative motion. On the basis of our results we propose a simple experiment which enables observers to determine locally whether their spacetime is described by a rotating Kerr or a non-rotating Schwarzschild metric. |
0711.4224 | Pop Adrian | Pop Adrian Alin | Perturbations for the Coulomb - Kepler problem on de Sitter space-time | 6 pages | null | null | null | gr-qc | null | In the Schrodinger picture of the Dirac quantum mechanics, defined in charts
with spatially flat Robertson-Walker metrics and Cartesian coordinates the
perturbation theory is applied to the interacting part of the Hamiltonian
operator produced by the minimal coupling with the gravitational field. First
and second order perturbations are computed.
| [
{
"created": "Tue, 27 Nov 2007 11:12:10 GMT",
"version": "v1"
}
] | 2007-11-28 | [
[
"Alin",
"Pop Adrian",
""
]
] | In the Schrodinger picture of the Dirac quantum mechanics, defined in charts with spatially flat Robertson-Walker metrics and Cartesian coordinates the perturbation theory is applied to the interacting part of the Hamiltonian operator produced by the minimal coupling with the gravitational field. First and second order perturbations are computed. |
1407.0340 | Serguei Krasnikov | S. Krasnikov | Yet another proof of Hawking and Ellis's Lemma 8.5.5 | A few misleading typos are corrected | Class. Quantum Grav. 31 (2014) 227001 | 10.1088/0264-9381/31/22/227001 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The fact that the null generators of a future Cauchy horizon are past
complete was proved first by Hawking and Ellis [1]. Then Budzy\'nski,
Kondracki, and Kr\'olak outlined a proof free from an error found in the
original one [2]. Finally, a week ago Minguzzi published his version of proof
[3] patching a previously unnoticed hole in the preceding two. I am not aware
of any flaws in that last proof, but it is quite difficult. In this note I
present a simpler one.
| [
{
"created": "Tue, 1 Jul 2014 18:11:38 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Oct 2014 12:21:16 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Krasnikov",
"S.",
""
]
] | The fact that the null generators of a future Cauchy horizon are past complete was proved first by Hawking and Ellis [1]. Then Budzy\'nski, Kondracki, and Kr\'olak outlined a proof free from an error found in the original one [2]. Finally, a week ago Minguzzi published his version of proof [3] patching a previously unnoticed hole in the preceding two. I am not aware of any flaws in that last proof, but it is quite difficult. In this note I present a simpler one. |
gr-qc/0608077 | Kourosh Nozari | Kourosh Nozari and Behnaz Fazlpour | Reissner-Nordstr\"{o}m Black Hole Thermodynamics in Noncommutative
Spaces | 13 pages, no figures, revised version | ActaPhys.Polon.B39:1363,2008; ActaPhys.Polon.B39:1363-1374,2008 | null | null | gr-qc | null | This paper considers the effects of space noncommutativity on the
thermodynamics of a Reissner-Nordstr\"{o}m black hole. In the first step, we
extend the ordinary formalism of Bekenstein-Hawking to the case of charged
black holes in commutative space. In the second step we investigate the effects
of space noncommutativity and the generalized uncertainty principle on the
thermodynamics of charged black holes. Finally we compare thermodynamics of
charged black holes in commutative space with thermodynamics of Schwarzschild
black hole in noncommutative space. In this comparison we explore some
conceptual relation between charge and space noncommutativity.
| [
{
"created": "Wed, 16 Aug 2006 09:41:35 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Dec 2006 11:30:18 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Nozari",
"Kourosh",
""
],
[
"Fazlpour",
"Behnaz",
""
]
] | This paper considers the effects of space noncommutativity on the thermodynamics of a Reissner-Nordstr\"{o}m black hole. In the first step, we extend the ordinary formalism of Bekenstein-Hawking to the case of charged black holes in commutative space. In the second step we investigate the effects of space noncommutativity and the generalized uncertainty principle on the thermodynamics of charged black holes. Finally we compare thermodynamics of charged black holes in commutative space with thermodynamics of Schwarzschild black hole in noncommutative space. In this comparison we explore some conceptual relation between charge and space noncommutativity. |
1507.02765 | Amir Babak Aazami | Amir Babak Aazami, Marcus C. Werner | The geometry of gravitational lensing magnification | 16 pages; v2: minor typos corrected | J. Geom. Phys. 100 (2016) | null | null | gr-qc astro-ph.GA math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a definition of unsigned magnification in gravitational lensing
valid on arbitrary convex normal neighborhoods of time oriented Lorentzian
manifolds. This definition is a function defined at any two points along a null
geodesic that lie in a convex normal neighborhood, and foregoes the usual
notions of lens and source planes in gravitational lensing. Rather, it makes
essential use of the van Vleck determinant, which we present via the
exponential map, and Etherington's definition of luminosity distance for
arbitrary spacetimes. We then specialize our definition to spacetimes, like
Schwarzschild's, in which the lens is compact and isolated, and show that our
magnification function is monotonically increasing along any geodesic contained
within a convex normal neighborhood.
| [
{
"created": "Fri, 10 Jul 2015 02:22:29 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Jan 2016 11:00:48 GMT",
"version": "v2"
}
] | 2016-01-22 | [
[
"Aazami",
"Amir Babak",
""
],
[
"Werner",
"Marcus C.",
""
]
] | We present a definition of unsigned magnification in gravitational lensing valid on arbitrary convex normal neighborhoods of time oriented Lorentzian manifolds. This definition is a function defined at any two points along a null geodesic that lie in a convex normal neighborhood, and foregoes the usual notions of lens and source planes in gravitational lensing. Rather, it makes essential use of the van Vleck determinant, which we present via the exponential map, and Etherington's definition of luminosity distance for arbitrary spacetimes. We then specialize our definition to spacetimes, like Schwarzschild's, in which the lens is compact and isolated, and show that our magnification function is monotonically increasing along any geodesic contained within a convex normal neighborhood. |
2404.01834 | Antonina Zinhailo | Alexey Dubinsky, Antonina Zinhailo | Asymptotic decay and quasinormal frequencies of scalar and Dirac fields
around dilaton-de Sitter black holes | 9 pages, 6 figures, 7 tables, revtex | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the decay of Dirac and massive scalar fields at asymptotically late
times in the background of the charged asymptotically de Sitter dilatonic black
holes. It is shown that the asymptotic decay is exponential and oscillatory for
large and intermediate mass of the field, while for zero and small mass it is
pure exponential without oscillations. This reflects the dominance of
quasinormal modes of the empty de Sitter spacetime at asymptotically late
times. We also show that the earlier WKB calculation of the massive scalar
field spectrum %[S. Fernando, Gen.Rel.Grav. 48 (2016) 3, 24] does not allow one
to find the fundamental mode with reasonable accuracy.
| [
{
"created": "Tue, 2 Apr 2024 10:47:01 GMT",
"version": "v1"
}
] | 2024-04-03 | [
[
"Dubinsky",
"Alexey",
""
],
[
"Zinhailo",
"Antonina",
""
]
] | We study the decay of Dirac and massive scalar fields at asymptotically late times in the background of the charged asymptotically de Sitter dilatonic black holes. It is shown that the asymptotic decay is exponential and oscillatory for large and intermediate mass of the field, while for zero and small mass it is pure exponential without oscillations. This reflects the dominance of quasinormal modes of the empty de Sitter spacetime at asymptotically late times. We also show that the earlier WKB calculation of the massive scalar field spectrum %[S. Fernando, Gen.Rel.Grav. 48 (2016) 3, 24] does not allow one to find the fundamental mode with reasonable accuracy. |
1609.08123 | Nirmalya Kajuri | Nirmalya Kajuri | Strong Equivalence Principle in Polymer Quantum Mechanics and deformed
Heisenberg Algebra | 7 pages, to appear in Phys. Rev. D | Phys. Rev. D 94, 084007 (2016) | 10.1103/PhysRevD.94.084007 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Strong equivalence Principle (SEP) states that the description of a
physical system in a gravitational field is indistinguishable from the
description of the same system at rest in an accelerating frame. While this
statement holds true in both General Relativity and ordinary Quantum Mechanics,
one expects it to fail when quantum gravity corrections are taken into account.
In this paper we investigate the possible failure of the SEP in two Quantum
Gravity inspired modifications of Quantum Mechanics - Polymer Quantum Mechanics
and deformed Heisenberg Algebra. We find that the SEP fails to hold in both
these theories. We estimate the deviation from SEP and find in both cases that
it is too small to be measured in present day experiments.
| [
{
"created": "Mon, 26 Sep 2016 19:04:18 GMT",
"version": "v1"
}
] | 2016-10-12 | [
[
"Kajuri",
"Nirmalya",
""
]
] | The Strong equivalence Principle (SEP) states that the description of a physical system in a gravitational field is indistinguishable from the description of the same system at rest in an accelerating frame. While this statement holds true in both General Relativity and ordinary Quantum Mechanics, one expects it to fail when quantum gravity corrections are taken into account. In this paper we investigate the possible failure of the SEP in two Quantum Gravity inspired modifications of Quantum Mechanics - Polymer Quantum Mechanics and deformed Heisenberg Algebra. We find that the SEP fails to hold in both these theories. We estimate the deviation from SEP and find in both cases that it is too small to be measured in present day experiments. |
gr-qc/0601037 | German Izquierdo | German Izquierdo | Relic gravitational waves and the cosmic accelerated expansion | 4 pages, 2 figures. Uses AIP style. To be published in the AIP
Proceedings of the XXVIII Spanish Relativity Meeting | null | 10.1063/1.2218213 | null | gr-qc | null | The possibility of reconstructing the whole history of the scale factor of
the Universe from the power spectrum of relic gravitational waves (RGWs) makes
the study of these waves quite interesting. First, we explore the impact of a
hypothetical era -right after reheating- dominated by mini black holes and
radiation that may lower the spectrum several orders of magnitude. Next, we
calculate the power spectrum of the RGWs taking into account the present stage
of accelerated expansion and an hypothetical second dust era. Finally, we study
the generalized second law of gravitational thermodynamics applied to the
present era of accelerated expansion of the Universe.
| [
{
"created": "Tue, 10 Jan 2006 10:59:05 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Izquierdo",
"German",
""
]
] | The possibility of reconstructing the whole history of the scale factor of the Universe from the power spectrum of relic gravitational waves (RGWs) makes the study of these waves quite interesting. First, we explore the impact of a hypothetical era -right after reheating- dominated by mini black holes and radiation that may lower the spectrum several orders of magnitude. Next, we calculate the power spectrum of the RGWs taking into account the present stage of accelerated expansion and an hypothetical second dust era. Finally, we study the generalized second law of gravitational thermodynamics applied to the present era of accelerated expansion of the Universe. |
1706.05466 | Chi-Yong Lin | Chen-Yu Liu, Da-Shin Lee, Chi-Yong Lin | Geodesic Motion of Neutral Particles around a Kerr-Newman Black Hole | Published version; 18 pages, 7 figures | Classical and Quantum Gravity 34, 235008 (2017) | 10.1088/1361-6382/aa903b | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the dynamics of a neutral particle around a Kerr-Newman black
hole, and in particular focus on the effects of the charge of the spinning
black hole on the motion of the particle. We first consider the innermost
stable circular orbits (ISCO) on the equatorial plane. It is found that the
presence of the charge of the black hole leads to the effective potential of
the particle with stronger repulsive effects as compared with the Kerr black
hole. As a result, the radius of ISCO decreases as charge $Q$ of the black hole
increases for a fixed value of black hole's angular momentum $a$. We then
consider a kick on the particle from its initial orbit out of the equatorial
motion. The perturbed motion of the particle will eventually be bounded, or
unbounded so that it escapes to spatial infinity. Even more, the particle will
likely be captured by the black hole. Thus we analytically and numerically
determine the parameter regions of the corresponding motions, in terms of the
initial radius of the orbital motion and the strength of the kick. The
comparison will be made with the motion of a neutral particle in the Kerr black
hole.
| [
{
"created": "Sat, 17 Jun 2017 01:13:49 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Nov 2017 13:39:04 GMT",
"version": "v2"
}
] | 2017-11-15 | [
[
"Liu",
"Chen-Yu",
""
],
[
"Lee",
"Da-Shin",
""
],
[
"Lin",
"Chi-Yong",
""
]
] | We examine the dynamics of a neutral particle around a Kerr-Newman black hole, and in particular focus on the effects of the charge of the spinning black hole on the motion of the particle. We first consider the innermost stable circular orbits (ISCO) on the equatorial plane. It is found that the presence of the charge of the black hole leads to the effective potential of the particle with stronger repulsive effects as compared with the Kerr black hole. As a result, the radius of ISCO decreases as charge $Q$ of the black hole increases for a fixed value of black hole's angular momentum $a$. We then consider a kick on the particle from its initial orbit out of the equatorial motion. The perturbed motion of the particle will eventually be bounded, or unbounded so that it escapes to spatial infinity. Even more, the particle will likely be captured by the black hole. Thus we analytically and numerically determine the parameter regions of the corresponding motions, in terms of the initial radius of the orbital motion and the strength of the kick. The comparison will be made with the motion of a neutral particle in the Kerr black hole. |
1001.4311 | David Craig | David A. Craig and Parampreet Singh | Consistent Histories in Quantum Cosmology | To appear in Foundations of Physics special issue on quantum
foundations | Found.Phys.41:371-379,2011 | 10.1007/s10701-010-9422-6 | PI-QG-171 | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We illustrate the crucial role played by decoherence (consistency of quantum
histories) in extracting consistent quantum probabilities for alternative
histories in quantum cosmology. Specifically, within a Wheeler-DeWitt
quantization of a flat Friedmann-Robertson-Walker cosmological model sourced
with a free massless scalar field, we calculate the probability that the
univese is singular in the sense that it assumes zero volume. Classical
solutions of this model are a disjoint set of expanding and contracting
singular branches. A naive assessment of the behavior of quantum states which
are superpositions of expanding and contracting universes may suggest that a
"quantum bounce" is possible i.e. that the wave function of the universe may
remain peaked on a non-singular classical solution throughout its history.
However, a more careful consistent histories analysis shows that for arbitrary
states in the physical Hilbert space the probability of this Wheeler-DeWitt
quantum universe encountering the big bang/crunch singularity is equal to
unity. A quantum Wheeler-DeWitt universe is inevitably singular, and a "quantum
bounce" is thus not possible in these models.
| [
{
"created": "Mon, 25 Jan 2010 20:51:17 GMT",
"version": "v1"
}
] | 2011-05-26 | [
[
"Craig",
"David A.",
""
],
[
"Singh",
"Parampreet",
""
]
] | We illustrate the crucial role played by decoherence (consistency of quantum histories) in extracting consistent quantum probabilities for alternative histories in quantum cosmology. Specifically, within a Wheeler-DeWitt quantization of a flat Friedmann-Robertson-Walker cosmological model sourced with a free massless scalar field, we calculate the probability that the univese is singular in the sense that it assumes zero volume. Classical solutions of this model are a disjoint set of expanding and contracting singular branches. A naive assessment of the behavior of quantum states which are superpositions of expanding and contracting universes may suggest that a "quantum bounce" is possible i.e. that the wave function of the universe may remain peaked on a non-singular classical solution throughout its history. However, a more careful consistent histories analysis shows that for arbitrary states in the physical Hilbert space the probability of this Wheeler-DeWitt quantum universe encountering the big bang/crunch singularity is equal to unity. A quantum Wheeler-DeWitt universe is inevitably singular, and a "quantum bounce" is thus not possible in these models. |
gr-qc/9604031 | Yuri Kubyshin | Yuri Kubyshin and Jerome Martin | On compatibility of the Kaluza-Klein approach with the COBE experiment | LaTeX, 9 pages, 1 Postscript figure, Extended version of the
contribution to the Proceedings of the Xth Workshop on High Energy Physics
and Quantum Field Theory, (Zvenigorod, Russia, 20-26 September, 1995) | null | null | FTUAM 96/16 | gr-qc | null | Contributions of primordial gravitational waves to the large-angular-scale
anisotropies of the cosmic microwave background radiation in multidimensional
cosmological models (Kaluza-Klein models) are studied. We derive limits on free
parameters of the models using results of the COBE experiment and other
astrophysical data. It is shown that in principle there is a room for
Kaluza-Klein models as possible candidates for the description of the Early
Universe. However, the obtained limits are very restrictive. Assuming that the
anisotropies are mostly due to gravitational waves, none of the concrete
models, analyzed in the article, satisfy them. On the other hand, if the
contribution of gravitational waves is very small then a string inspired model
is not ruled out.
| [
{
"created": "Mon, 15 Apr 1996 11:17:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kubyshin",
"Yuri",
""
],
[
"Martin",
"Jerome",
""
]
] | Contributions of primordial gravitational waves to the large-angular-scale anisotropies of the cosmic microwave background radiation in multidimensional cosmological models (Kaluza-Klein models) are studied. We derive limits on free parameters of the models using results of the COBE experiment and other astrophysical data. It is shown that in principle there is a room for Kaluza-Klein models as possible candidates for the description of the Early Universe. However, the obtained limits are very restrictive. Assuming that the anisotropies are mostly due to gravitational waves, none of the concrete models, analyzed in the article, satisfy them. On the other hand, if the contribution of gravitational waves is very small then a string inspired model is not ruled out. |
2407.17984 | Theodore Anton | Theodore Anton | Relativistic gravity in the inhomogeneous Universe | PhD thesis, 325 pages. Defended 24th June 2024 | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmology is built on a relativistic understanding of gravity, where the
geometry of the Universe is dynamically determined by matter and energy. In the
cosmological concordance model, gravity is described by General Relativity, and
it is assumed that on large scales the Universe is homogeneous and isotropic.
These fundamental principles should be tested. In this thesis, we explore the
implications of breaking them.
In order to understand possible modifications to gravity on cosmological
scales, we extend the formalism of parameterised post-Newtonian cosmology, an
approach for building cosmological tests of gravity that are consistent with
tests on astrophysical scales. We demonstrate how this approach can be used to
construct theory-independent equations for the cosmic expansion and its
first-order perturbations. Then, we apply the framework to observations of the
anisotropies in the cosmic microwave background. We use these to place novel
cosmological constraints on the evolution of the post-Newtonian parameters.
We investigate the consequences of inhomogeneity and isotropy by developing a
new approach to studying anisotropy in the Universe, wherein we consider how an
anisotropic cosmology might emerge on large scales as a result of averaging
over inhomogeneous structures, and demonstrate how the emergent model is
affected by backreaction. We perform a detailed study of light propagation in a
wide class of inhomogeneous and anisotropic spacetimes, exploring the
conditions under which the Hubble diagram can be accurately predicted by an
anisotropic model constructed using explicit averaging, even in the presence of
large inhomogeneities. We show that observables calculated in a suitable
averaged description closely reproduce the true Hubble diagram on large scales,
as long as the spacetime possesses a well-defined homogeneity scale.
| [
{
"created": "Thu, 25 Jul 2024 12:17:45 GMT",
"version": "v1"
}
] | 2024-07-26 | [
[
"Anton",
"Theodore",
""
]
] | Cosmology is built on a relativistic understanding of gravity, where the geometry of the Universe is dynamically determined by matter and energy. In the cosmological concordance model, gravity is described by General Relativity, and it is assumed that on large scales the Universe is homogeneous and isotropic. These fundamental principles should be tested. In this thesis, we explore the implications of breaking them. In order to understand possible modifications to gravity on cosmological scales, we extend the formalism of parameterised post-Newtonian cosmology, an approach for building cosmological tests of gravity that are consistent with tests on astrophysical scales. We demonstrate how this approach can be used to construct theory-independent equations for the cosmic expansion and its first-order perturbations. Then, we apply the framework to observations of the anisotropies in the cosmic microwave background. We use these to place novel cosmological constraints on the evolution of the post-Newtonian parameters. We investigate the consequences of inhomogeneity and isotropy by developing a new approach to studying anisotropy in the Universe, wherein we consider how an anisotropic cosmology might emerge on large scales as a result of averaging over inhomogeneous structures, and demonstrate how the emergent model is affected by backreaction. We perform a detailed study of light propagation in a wide class of inhomogeneous and anisotropic spacetimes, exploring the conditions under which the Hubble diagram can be accurately predicted by an anisotropic model constructed using explicit averaging, even in the presence of large inhomogeneities. We show that observables calculated in a suitable averaged description closely reproduce the true Hubble diagram on large scales, as long as the spacetime possesses a well-defined homogeneity scale. |
gr-qc/9311017 | Domenico Giulini | Domenico Giulini | What is the Geometry of Superspace ? | 10 pages, Plain Tex | Phys.Rev.D51:5630-5635,1995 | 10.1103/PhysRevD.51.5630 | null | gr-qc | null | We investigate certain properties of the Wheeler-DeWitt metric (for constant
lapse) in canonical General Relativity associated with its non-definite nature.
Contribution to the conference on Mach's principle: "From Newtons Bucket to
Quantum Gravity", July 26-30 1993, Tuebingen, Germany
| [
{
"created": "Wed, 10 Nov 1993 21:49:38 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Giulini",
"Domenico",
""
]
] | We investigate certain properties of the Wheeler-DeWitt metric (for constant lapse) in canonical General Relativity associated with its non-definite nature. Contribution to the conference on Mach's principle: "From Newtons Bucket to Quantum Gravity", July 26-30 1993, Tuebingen, Germany |
gr-qc/0702016 | Bernard Kelly | Dae-Il Choi, Bernard J. Kelly, William D. Boggs, John G. Baker, Joan
Centrella, James van Meter | Recoiling from a kick in the head-on collision of spinning black holes | 12 pages, 10 figures. Replaced with published version, including more
discussion of convergence and properties of final hole | Phys.Rev.D76:104026,2007 | 10.1103/PhysRevD.76.104026 | null | gr-qc | null | Recoil ``kicks'' induced by gravitational radiation are expected in the
inspiral and merger of black holes. Recently the numerical relativity community
has begun to measure the significant kicks found when both unequal masses and
spins are considered. Because understanding the cause and magnitude of each
component of this kick may be complicated in inspiral simulations, we consider
these effects in the context of a simple test problem. We study recoils from
collisions of binaries with initially head-on trajectories, starting with the
simplest case of equal masses with no spin and then adding spin and varying the
mass ratio, both separately and jointly. We find spin-induced recoils to be
significant relative to unequal-mass recoils even in head-on configurations.
Additionally, it appears that the scaling of transverse kicks with spins is
consistent with post-Newtonian theory, even though the kick is generated in the
nonlinear merger interaction, where post-Newtonian theory should not apply.
This suggests that a simple heuristic description might be effective in the
estimation of spin-kicks.
| [
{
"created": "Fri, 2 Feb 2007 20:55:18 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Nov 2007 20:36:39 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Choi",
"Dae-Il",
""
],
[
"Kelly",
"Bernard J.",
""
],
[
"Boggs",
"William D.",
""
],
[
"Baker",
"John G.",
""
],
[
"Centrella",
"Joan",
""
],
[
"van Meter",
"James",
""
]
] | Recoil ``kicks'' induced by gravitational radiation are expected in the inspiral and merger of black holes. Recently the numerical relativity community has begun to measure the significant kicks found when both unequal masses and spins are considered. Because understanding the cause and magnitude of each component of this kick may be complicated in inspiral simulations, we consider these effects in the context of a simple test problem. We study recoils from collisions of binaries with initially head-on trajectories, starting with the simplest case of equal masses with no spin and then adding spin and varying the mass ratio, both separately and jointly. We find spin-induced recoils to be significant relative to unequal-mass recoils even in head-on configurations. Additionally, it appears that the scaling of transverse kicks with spins is consistent with post-Newtonian theory, even though the kick is generated in the nonlinear merger interaction, where post-Newtonian theory should not apply. This suggests that a simple heuristic description might be effective in the estimation of spin-kicks. |
gr-qc/0307015 | Pablo Laguna | U. Sperhake, K.L. Smith, B. Kelly, P. Laguna and D. Shoemaker | Impact of densitized lapse slicings on evolutions of a wobbling black
hole | 10 pages, 8 figures | Phys.Rev.D69:024012,2004 | 10.1103/PhysRevD.69.024012 | null | gr-qc | null | We present long-term stable and second-order convergent evolutions of an
excised wobbling black hole. Our results clearly demonstrate that the use of a
densitized lapse function extends the lifetime of simulations dramatically. We
also show the improvement in the stability of single static black holes when an
algebraic densitized lapse condition is applied. In addition, we introduce a
computationally inexpensive approach for tracking the location of the
singularity suitable for mildly distorted black holes. The method is based on
investigating the fall-off behavior and asymmetry of appropriate grid
variables. This simple tracking method allows one to adjust the location of the
excision region to follow the coordinate motion of the singularity.
| [
{
"created": "Thu, 3 Jul 2003 21:15:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Sperhake",
"U.",
""
],
[
"Smith",
"K. L.",
""
],
[
"Kelly",
"B.",
""
],
[
"Laguna",
"P.",
""
],
[
"Shoemaker",
"D.",
""
]
] | We present long-term stable and second-order convergent evolutions of an excised wobbling black hole. Our results clearly demonstrate that the use of a densitized lapse function extends the lifetime of simulations dramatically. We also show the improvement in the stability of single static black holes when an algebraic densitized lapse condition is applied. In addition, we introduce a computationally inexpensive approach for tracking the location of the singularity suitable for mildly distorted black holes. The method is based on investigating the fall-off behavior and asymmetry of appropriate grid variables. This simple tracking method allows one to adjust the location of the excision region to follow the coordinate motion of the singularity. |
2405.09791 | Peiran Yin | Peiran Yin, Rui Li, Chengjiang Yin, Xiangyu Xu, Xiang Bian, Han Xie,
Chang-Kui Duan, Pu Huang, Jian-hua He, Jiangfeng Du | Challenging theories of dark energy with levitated force sensor | null | Nature Physics 18, 1181-1185 (2022) | 10.1038/s41567-022-01706-9 | null | gr-qc astro-ph.IM physics.ins-det | http://creativecommons.org/licenses/by-nc-sa/4.0/ | The nature of dark energy is one of the most outstanding problems in physical
science, and various theories have been proposed. It is therefore essential to
directly verify or rule out these theories experimentally. However, despite
substantial efforts in astrophysical observations and laboratory experiments,
previous tests have not yet acquired enough accuracy to provide decisive
conclusions as to the validity of these theories. Here, using a diamagnetically
levitated force sensor, we carry out a test on one of the most compelling
explanations for dark energy to date, namely the Chameleon theory, an
ultra-light scalar field with screening mechanisms, which couples to
normal-matter fields and leaves a detectable fifth force. Our results extend
previous results by nearly two orders of magnitude to the entire physical
plausible parameter space of cosmologically viable chameleon models. We find no
evidence for such a fifth force. Our results decisively rule out the basic
chameleon model as a candidate for dark energy. Our work, thus, demonstrates
the robustness of laboratory experiments in unveiling the nature of dark energy
in the future. The methodology developed here can be further applied to study a
broad range of fundamental physics.
| [
{
"created": "Thu, 16 May 2024 03:42:15 GMT",
"version": "v1"
}
] | 2024-05-17 | [
[
"Yin",
"Peiran",
""
],
[
"Li",
"Rui",
""
],
[
"Yin",
"Chengjiang",
""
],
[
"Xu",
"Xiangyu",
""
],
[
"Bian",
"Xiang",
""
],
[
"Xie",
"Han",
""
],
[
"Duan",
"Chang-Kui",
""
],
[
"Huang",
"Pu",
""
],
[
"He",
"Jian-hua",
""
],
[
"Du",
"Jiangfeng",
""
]
] | The nature of dark energy is one of the most outstanding problems in physical science, and various theories have been proposed. It is therefore essential to directly verify or rule out these theories experimentally. However, despite substantial efforts in astrophysical observations and laboratory experiments, previous tests have not yet acquired enough accuracy to provide decisive conclusions as to the validity of these theories. Here, using a diamagnetically levitated force sensor, we carry out a test on one of the most compelling explanations for dark energy to date, namely the Chameleon theory, an ultra-light scalar field with screening mechanisms, which couples to normal-matter fields and leaves a detectable fifth force. Our results extend previous results by nearly two orders of magnitude to the entire physical plausible parameter space of cosmologically viable chameleon models. We find no evidence for such a fifth force. Our results decisively rule out the basic chameleon model as a candidate for dark energy. Our work, thus, demonstrates the robustness of laboratory experiments in unveiling the nature of dark energy in the future. The methodology developed here can be further applied to study a broad range of fundamental physics. |
1309.0552 | Jerzy Matyjasek | Jerzy Matyjasek and Pawe{\l} Sadurski | Stress-Energy Tensor of the Quantized Massive Fields in
Friedman-Robertson-Walker Spacetimes | Section III expanded. References added. Matches published version | Phys. Rev. D 88, 104015 (2013) | 10.1103/PhysRevD.88.104015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The approximate stress-energy tensor of the quantized massive scalar, spinor
and vector fields in the spatially flat Friedman-Robertson-Walker universe is
constructed. It is shown that for the scalar fields with arbitrary curvature
coupling, $\xi,$ the stress-energy tensor calculated within the framework of
the Schwinger-DeWitt approach is identical to the analogous tensor constructed
in the adiabatic vacuum. Similarly, the Schwinger-DeWitt stress-energy tensor
for the fields of spin 1/2 and 1 coincides with the analogous result calculated
by the Zeldovich-Starobinsky method. The stress-energy tensor thus obtained are
subsequently used in the back reaction problem. It is shown that for pure
semiclassical Einstein field equations with the vanishing cosmological constant
and the source term consisting exclusively of its quantum part there are no
self-consistent exponential solutions driven by the spinor and vector fields. A
similar situation takes place for the scalar field if the coupling constant
belongs to the interval $\xi \gtrsim 0.1.$ For a positive cosmological constant
the expansion slows down for all considered types of massive fields except for
minimally coupled scalar field. The perturbative approach to the problem is
briefly discussed and possible generalizations of the stress-energy tensor are
indicated.
| [
{
"created": "Mon, 2 Sep 2013 22:12:18 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Nov 2013 10:56:02 GMT",
"version": "v2"
}
] | 2013-11-19 | [
[
"Matyjasek",
"Jerzy",
""
],
[
"Sadurski",
"Paweł",
""
]
] | The approximate stress-energy tensor of the quantized massive scalar, spinor and vector fields in the spatially flat Friedman-Robertson-Walker universe is constructed. It is shown that for the scalar fields with arbitrary curvature coupling, $\xi,$ the stress-energy tensor calculated within the framework of the Schwinger-DeWitt approach is identical to the analogous tensor constructed in the adiabatic vacuum. Similarly, the Schwinger-DeWitt stress-energy tensor for the fields of spin 1/2 and 1 coincides with the analogous result calculated by the Zeldovich-Starobinsky method. The stress-energy tensor thus obtained are subsequently used in the back reaction problem. It is shown that for pure semiclassical Einstein field equations with the vanishing cosmological constant and the source term consisting exclusively of its quantum part there are no self-consistent exponential solutions driven by the spinor and vector fields. A similar situation takes place for the scalar field if the coupling constant belongs to the interval $\xi \gtrsim 0.1.$ For a positive cosmological constant the expansion slows down for all considered types of massive fields except for minimally coupled scalar field. The perturbative approach to the problem is briefly discussed and possible generalizations of the stress-energy tensor are indicated. |
2301.04448 | Hrvoje Nikolic | Hrvoje Nikolic | Emergent diffeomorphism invariance in toy models | 21 pages, accepted for publication in Fortsch. Phys | Fortschr. Phys. 71, 2300026 (2023) | 10.1002/prop.202300026 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Conceptual difficulties in semiclassical and quantum gravity arise from
diffeomorphism invariance of classical general relativity. With a motivation to
shed some light on these difficulties, we study a class of toy models for which
one-dimensional diffeomorphism invariance, namely time-reparametrization
invariance, emerges at the classical level from energy conservation. An attempt
to quantize the models while taking the invariance seriously leads to toy
versions of the problem of time in quantum gravity, of the cosmological
constant problem, and of the black hole firewall problem. Nevertheless, all
these problems are easily resolved by taking into account that the invariance
emerges only at the classical level, while the fundamental theory that needs to
be quantized is not diffeomorphism invariant.
| [
{
"created": "Wed, 11 Jan 2023 13:08:55 GMT",
"version": "v1"
},
{
"created": "Mon, 15 May 2023 12:45:23 GMT",
"version": "v2"
}
] | 2023-09-07 | [
[
"Nikolic",
"Hrvoje",
""
]
] | Conceptual difficulties in semiclassical and quantum gravity arise from diffeomorphism invariance of classical general relativity. With a motivation to shed some light on these difficulties, we study a class of toy models for which one-dimensional diffeomorphism invariance, namely time-reparametrization invariance, emerges at the classical level from energy conservation. An attempt to quantize the models while taking the invariance seriously leads to toy versions of the problem of time in quantum gravity, of the cosmological constant problem, and of the black hole firewall problem. Nevertheless, all these problems are easily resolved by taking into account that the invariance emerges only at the classical level, while the fundamental theory that needs to be quantized is not diffeomorphism invariant. |
1008.0524 | James D. E. Grant | James D. E. Grant | Areas and volumes for null cones | 16 pages, no figures. Typos fixed. One garbled proof corrected.
Published version | Annales Henri Poincare 12:965-985,2011 | 10.1007/s00023-011-0090-7 | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by recent work of Choquet-Bruhat, Chrusciel, and Martin-Garcia, we
prove monotonicity properties and comparison results for the area of slices of
the null cone of a point in a Lorentzian manifold. We also prove volume
comparison results for subsets of the null cone analogous to the Bishop-Gromov
relative volume monotonicity theorem and Guenther's volume comparison theorem.
We briefly discuss how these estimates may be used to control the null second
fundamental form of slices of the null cone in Ricci-flat Lorentzian
four-manifolds with null curvature bounded above.
| [
{
"created": "Tue, 3 Aug 2010 11:38:07 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Dec 2011 08:42:13 GMT",
"version": "v2"
}
] | 2011-12-02 | [
[
"Grant",
"James D. E.",
""
]
] | Motivated by recent work of Choquet-Bruhat, Chrusciel, and Martin-Garcia, we prove monotonicity properties and comparison results for the area of slices of the null cone of a point in a Lorentzian manifold. We also prove volume comparison results for subsets of the null cone analogous to the Bishop-Gromov relative volume monotonicity theorem and Guenther's volume comparison theorem. We briefly discuss how these estimates may be used to control the null second fundamental form of slices of the null cone in Ricci-flat Lorentzian four-manifolds with null curvature bounded above. |
2312.05266 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | On the status of wormholes in Einstein's theory | 18 pages, no figures | Letters in High Energy Physics (LHEP), vol. 2023, ID: 469, 2023 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been claimed that wormholes are just as good a prediction of
Einstein's theory as black holes, but they are subject to severe restrictions
from quantum field theory. The purpose of this paper is to show that the claim
can be substantiated in spite of these restrictions.
| [
{
"created": "Wed, 6 Dec 2023 12:48:20 GMT",
"version": "v1"
}
] | 2023-12-12 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | It has been claimed that wormholes are just as good a prediction of Einstein's theory as black holes, but they are subject to severe restrictions from quantum field theory. The purpose of this paper is to show that the claim can be substantiated in spite of these restrictions. |
gr-qc/9801091 | Cristian Martinez | Cristian Martinez | Instability of three dimensional conformally dressed black hole | 5 pages, REVTeX | Phys.Rev. D58 (1998) 027501 | 10.1103/PhysRevD.58.027501 | null | gr-qc | null | The three dimensional black hole solution of Einstein equations with negative
cosmological constant coupled to a conformal scalar field is proved to be
unstable against linear circularly symmetric perturbations.
| [
{
"created": "Tue, 27 Jan 1998 15:46:46 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Martinez",
"Cristian",
""
]
] | The three dimensional black hole solution of Einstein equations with negative cosmological constant coupled to a conformal scalar field is proved to be unstable against linear circularly symmetric perturbations. |
0905.2502 | Christian Corda | Christian Corda | Interferometric detection of gravitational waves: the definitive test
for General Relativity | This Essay is an Honorable Mention Winner at the 2009 Gravity
Research Foundation Awards | Int. J. Mod. Phys. D18:2275-2282,2009 | 10.1142/S0218271809015904 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Even if Einstein's General Relativity achieved a great success and overcame
lots of experimental tests, it also showed some shortcomings and flaws which
today advise theorists to ask if it is the definitive theory of gravity. In
this essay we show that, if advanced projects on the detection of Gravitational
Waves (GWs) will improve their sensitivity, allowing to perform a GWs
astronomy, accurate angular and frequency dependent response functions of
interferometers for GWs arising from various Theories of Gravity, i.e. General
Relativity and Extended Theories of Gravity, will be the definitive test for
General Relativity. The papers which found this essay have been the world's
most cited in the official Astroparticle Publication Review of ASPERA during
the 2007 with 13 citations.
| [
{
"created": "Fri, 15 May 2009 10:01:24 GMT",
"version": "v1"
},
{
"created": "Wed, 27 May 2009 15:52:41 GMT",
"version": "v2"
},
{
"created": "Mon, 8 Jun 2009 14:45:09 GMT",
"version": "v3"
}
] | 2010-04-21 | [
[
"Corda",
"Christian",
""
]
] | Even if Einstein's General Relativity achieved a great success and overcame lots of experimental tests, it also showed some shortcomings and flaws which today advise theorists to ask if it is the definitive theory of gravity. In this essay we show that, if advanced projects on the detection of Gravitational Waves (GWs) will improve their sensitivity, allowing to perform a GWs astronomy, accurate angular and frequency dependent response functions of interferometers for GWs arising from various Theories of Gravity, i.e. General Relativity and Extended Theories of Gravity, will be the definitive test for General Relativity. The papers which found this essay have been the world's most cited in the official Astroparticle Publication Review of ASPERA during the 2007 with 13 citations. |
2310.02958 | Aron Wall | Aron C. Wall | What if Quantum Gravity is "just'' Quantum Information Theory? | 6 pages, 2 figures. Additional references added to arxiv version | Proc. 28th Solvay Conf. Phys., ed. D. Gross, A. Sevrin, P. Zoller,
World Scientific Publishing Co., Singapore, 2023 | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I suggest the possibility that holographic quantum gravity is, in some sense,
equivalent to quantum information theory. Some radical implications would
follow. First, the theory of quantum gravity should have no adjustable coupling
constants, similar to string theory. Thus, all complete bulk theories of
quantum gravity are dual to each other. By setting up an appropriately
entangled state, it should be possible to find wormholes connecting any two
quantum gravity theories (e.g. string theory and loop quantum gravity).
Secondly, if we represent space at one time as a tensor network, then dynamics
is automatically encoded via gauge-equivalent descriptions of the boundary
state. This would appear to imply, contrary to semiclassical expectations, that
a closed universe should have only one state.
| [
{
"created": "Wed, 4 Oct 2023 16:48:10 GMT",
"version": "v1"
}
] | 2023-10-05 | [
[
"Wall",
"Aron C.",
""
]
] | I suggest the possibility that holographic quantum gravity is, in some sense, equivalent to quantum information theory. Some radical implications would follow. First, the theory of quantum gravity should have no adjustable coupling constants, similar to string theory. Thus, all complete bulk theories of quantum gravity are dual to each other. By setting up an appropriately entangled state, it should be possible to find wormholes connecting any two quantum gravity theories (e.g. string theory and loop quantum gravity). Secondly, if we represent space at one time as a tensor network, then dynamics is automatically encoded via gauge-equivalent descriptions of the boundary state. This would appear to imply, contrary to semiclassical expectations, that a closed universe should have only one state. |
1410.2069 | Iver Brevik | Iver Brevik | Brane Viscous Cosmology in the Plasma Era | 8 pages, no figures; to appear in Astrophys. Space Sci | Astrophysics and Space Science 355, 179-185 (2015) | 10.1007/s10509-014-2162-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider how the five-dimensional Randall-Sundrum (one-brane) theory
becomes modified when account is taken of the bulk viscosity of the cosmic
fluid on the brane. We focus on the plasma era between $10^{12}$K (muon pair
annihilation) to about $5\times 10^9$K (electron-positron annihilation), which
includes the first order quark-hadron transition beginning at an energy density
of about $5\times 10^9\rm MeV^4$. Various possibilities are examined for
modeling the bulk viscosity, preference being at the end given to the results
calculated from relativistic kinetic theory. According to this, the viscosity
is negligible at the highest temperatures, but may amount to a few per cent
corrections in the later stages of the plasma era. We also briefly consider
anisotropic universes where the shear viscosity comes into play, and show that
in the case of the Kasner model the influences from bulk viscosity and shear
viscosity become comparable when the anisotropy parameter of the universe is of
order $A \sim 10^{-11} $ in the beginning of the plasma era, and $A \sim
10^{-2}$ in its later region.
| [
{
"created": "Wed, 8 Oct 2014 11:52:26 GMT",
"version": "v1"
}
] | 2015-02-23 | [
[
"Brevik",
"Iver",
""
]
] | We consider how the five-dimensional Randall-Sundrum (one-brane) theory becomes modified when account is taken of the bulk viscosity of the cosmic fluid on the brane. We focus on the plasma era between $10^{12}$K (muon pair annihilation) to about $5\times 10^9$K (electron-positron annihilation), which includes the first order quark-hadron transition beginning at an energy density of about $5\times 10^9\rm MeV^4$. Various possibilities are examined for modeling the bulk viscosity, preference being at the end given to the results calculated from relativistic kinetic theory. According to this, the viscosity is negligible at the highest temperatures, but may amount to a few per cent corrections in the later stages of the plasma era. We also briefly consider anisotropic universes where the shear viscosity comes into play, and show that in the case of the Kasner model the influences from bulk viscosity and shear viscosity become comparable when the anisotropy parameter of the universe is of order $A \sim 10^{-11} $ in the beginning of the plasma era, and $A \sim 10^{-2}$ in its later region. |
2306.10445 | Zhoujian Cao Dr | Li-Fang Li and Zhoujian Cao | Post-Keplerian waveform model for binary compact object as sources of
space-based gravitational wave detector and its implications | 14 pages, 3 figures | General Relativity and Gravitation, 55, 76 (2023) | 10.1007/s10714-023-03123-6 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Binary compact objects will be among the important sources for the future
space-based gravitational wave detectors. Such binary compact objects include
stellar massive binary black hole, binary neutron star, binary white dwarf and
mixture of these compact objects. Regarding to the relatively low frequency,
the gravitational interaction between the two objects of the binary is weak.
Post-Newtonian approximation of general relativity is valid. Previous works
about the waveform model for such binaries in the literature consider the
dynamics for specific situations which involve detailed complicated matter
dynamics between the two objects. We here take a different idea. We adopt the
trick used in pulsar timing detection. For any gravity theories and any
detailed complicated matter dynamics, the motion of the binary can always be
described as a post-Keplerian expansion. And a post-Keplerian gravitational
waveform model will be reduced. Instead of object masses, spins, matter's
equation of state parameters and dynamical parameters beyond general
relativity, the involved parameters in our post-Keplerian waveform model are
the Keplerian orbit elements and their adiabatic variations. Respect to current
planning space-based gravitational wave detectors including LISA, Taiji and
Tianqin, we find that the involved waveform model parameters can be well
determined. And consequently the detail matter dynamics of the binary can be
studied then. For binary with purely gravitational interactions, gravity theory
can be constrained well.
| [
{
"created": "Sun, 18 Jun 2023 00:45:06 GMT",
"version": "v1"
}
] | 2023-06-21 | [
[
"Li",
"Li-Fang",
""
],
[
"Cao",
"Zhoujian",
""
]
] | Binary compact objects will be among the important sources for the future space-based gravitational wave detectors. Such binary compact objects include stellar massive binary black hole, binary neutron star, binary white dwarf and mixture of these compact objects. Regarding to the relatively low frequency, the gravitational interaction between the two objects of the binary is weak. Post-Newtonian approximation of general relativity is valid. Previous works about the waveform model for such binaries in the literature consider the dynamics for specific situations which involve detailed complicated matter dynamics between the two objects. We here take a different idea. We adopt the trick used in pulsar timing detection. For any gravity theories and any detailed complicated matter dynamics, the motion of the binary can always be described as a post-Keplerian expansion. And a post-Keplerian gravitational waveform model will be reduced. Instead of object masses, spins, matter's equation of state parameters and dynamical parameters beyond general relativity, the involved parameters in our post-Keplerian waveform model are the Keplerian orbit elements and their adiabatic variations. Respect to current planning space-based gravitational wave detectors including LISA, Taiji and Tianqin, we find that the involved waveform model parameters can be well determined. And consequently the detail matter dynamics of the binary can be studied then. For binary with purely gravitational interactions, gravity theory can be constrained well. |
gr-qc/9409026 | null | Juan Garcia-Bellido | Quantum Fluctuations of Planck Mass as Mutation Mechanism in a Theory of
Evolution of the Universe | 3 pages, Stanford University preprint SU-ITP-94-32, IEM-FT-92/94 | null | null | null | gr-qc astro-ph | null | Contributed talk at the Seventh Marcel Grossman Meeting on Gravity, June
24-30. A theory of evolution of the universe requires both a mutation mechanism
and a selection mechanism. We believe that both can be encountered in the
stochastic approach to quantum cosmology. In Brans-Dicke chaotic inflation, the
quantum fluctuations of Planck mass behave as mutations, such that new
inflationary domains may contain values of Planck mass that differ slightly
from their parent's. The selection mechanism establishes that the value of
Planck mass should be such as to increase the proper volume of the inflationary
domain, which will then generate more offsprings. This mechanism predicts that
the effective Planck scale at the end of inflation should be much larger than
any given scale in the model.
| [
{
"created": "Tue, 13 Sep 1994 21:06:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Garcia-Bellido",
"Juan",
""
]
] | Contributed talk at the Seventh Marcel Grossman Meeting on Gravity, June 24-30. A theory of evolution of the universe requires both a mutation mechanism and a selection mechanism. We believe that both can be encountered in the stochastic approach to quantum cosmology. In Brans-Dicke chaotic inflation, the quantum fluctuations of Planck mass behave as mutations, such that new inflationary domains may contain values of Planck mass that differ slightly from their parent's. The selection mechanism establishes that the value of Planck mass should be such as to increase the proper volume of the inflationary domain, which will then generate more offsprings. This mechanism predicts that the effective Planck scale at the end of inflation should be much larger than any given scale in the model. |
1809.10412 | Matt Visser | Ivan Booth (University of Newfoundland), Bradley Creelman (University
of Newfoundland), Jessica Santiago (Victoria University of Wellington), and
Matt Visser (Victoria University of Wellington) | Evading the Trans-Planckian problem with Vaidya spacetimes | 32 pages; 5 figures | null | 10.1088/1475-7516/2019/09/067 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hawking radiation, when treated in the ray optics limit, exhibits the
unfortunate trans-Planckian problem --- a Hawking photon near spatial infinity,
if back-tracked to the immediate vicinity of the horizon is hugely blue-shifted
and found to have had trans-Planckian energy. (And if back-tracked all the way
to the horizon, the photon is formally infinitely blue-shifted, and formally
acquires infinite energy.) Unruh has forcefully argued that this implies that
the Hawking flux represents a vacuum instability in the presence of a horizon,
and that the Hawking photons are actually emitted from some region exterior to
the horizon. We seek to make this idea more precise and somewhat explicit by
building a purely kinematical model for Hawking evaporation based on two Vaidya
spacetimes (outer and inner) joined across a thin time-like boundary layer. The
kinematics of this model is already quite rich, and we shall defer
consideration of the dynamics for subsequent work. In particular we shall
present an explicit calculation of the the 4-acceleration of the shell
(including the effects of gravity, motion, and the outgoing null flux) and
relate this 4-acceleration to the Unruh temperature.
| [
{
"created": "Thu, 27 Sep 2018 09:00:37 GMT",
"version": "v1"
}
] | 2019-10-09 | [
[
"Booth",
"Ivan",
"",
"University of Newfoundland"
],
[
"Creelman",
"Bradley",
"",
"University\n of Newfoundland"
],
[
"Santiago",
"Jessica",
"",
"Victoria University of Wellington"
],
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] | Hawking radiation, when treated in the ray optics limit, exhibits the unfortunate trans-Planckian problem --- a Hawking photon near spatial infinity, if back-tracked to the immediate vicinity of the horizon is hugely blue-shifted and found to have had trans-Planckian energy. (And if back-tracked all the way to the horizon, the photon is formally infinitely blue-shifted, and formally acquires infinite energy.) Unruh has forcefully argued that this implies that the Hawking flux represents a vacuum instability in the presence of a horizon, and that the Hawking photons are actually emitted from some region exterior to the horizon. We seek to make this idea more precise and somewhat explicit by building a purely kinematical model for Hawking evaporation based on two Vaidya spacetimes (outer and inner) joined across a thin time-like boundary layer. The kinematics of this model is already quite rich, and we shall defer consideration of the dynamics for subsequent work. In particular we shall present an explicit calculation of the the 4-acceleration of the shell (including the effects of gravity, motion, and the outgoing null flux) and relate this 4-acceleration to the Unruh temperature. |
gr-qc/9611029 | Jose Acacio de Barros | J. Acacio de Barros (Physics Department/UFJF, Brazil) and N.
Pinto-Neto (CBPF/Lafex, Brazil) | Comments on the Quantum Potential Approach to a Class of Quantum
Cosmological Models | 7 pages, LaTeX | Class.Quant.Grav. 14 (1997) 1993-1995 | 10.1088/0264-9381/14/7/030 | null | gr-qc quant-ph | null | In this comment we bring attention to the fact that when we apply the
ontological interpretation of quantum mechanics, we must be sure to use it in
the coordinate representation. This is particularly important when canonical
tranformations that mix momenta and coordinates are present. This implies that
some of the results obtained by A. B\l aut and J. Kowalski-Glikman are
incorrect.
| [
{
"created": "Mon, 11 Nov 1996 19:11:38 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"de Barros",
"J. Acacio",
"",
"Physics Department/UFJF, Brazil"
],
[
"Pinto-Neto",
"N.",
"",
"CBPF/Lafex, Brazil"
]
] | In this comment we bring attention to the fact that when we apply the ontological interpretation of quantum mechanics, we must be sure to use it in the coordinate representation. This is particularly important when canonical tranformations that mix momenta and coordinates are present. This implies that some of the results obtained by A. B\l aut and J. Kowalski-Glikman are incorrect. |
1801.01350 | Giovanni Camelio | Giovanni Camelio | Early evolution of newly born proto-neutron stars | Minor modification to my PhD thesis. Partial overlap with
arXiv:1601.02945 [Camelio et al., PRD, 2016] and arXiv:1704.01923 [Camelio et
al., PRD, 2017]. Original version available at:
http://hdl.handle.net/11573/942744 | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A proto-neutron star (PNS) is the first phase of life of a neutron star, and
is likely to origin from a core-collapse supernova. After about 200 ms from
core-collapse, the PNS evolution may be modeled as a sequence of
quasi-stationary configurations. These configurations depend on the PNS
thermodynamic profiles, whose evolution largely depends upon the neutrino
diffusion. We developed a new PNS evolutionary code that solves by iteration
the neutrino number and energy transport equations together with the
relativistic stellar structure equations assuming spherical symmetry. The
neutrino cross sections are determined consistently with the underlying
equation of state (EoS). To include the EoSs in the evolution, we devised and
tested a new fitting formula for the interacting part of the baryon
free-energy, valid at finite temperature and arbitrary degeneracy. Using our
code, we provide estimates for the neutrino signal in the Super-Kamiokande III
detector and the frequencies of the gravitational waves due to stellar
oscillations, for three stellar masses and three nucleonic EoSs. For the first
time we evolve a PNS with a nuclear many-body theory EoS in a consistent way,
that is, we take into account realistic nuclear interactions in the computation
of the neutrino cross sections. By including rotation in an effective way, we
have also determined the time variation of the rotation frequency due to PNS
contraction and neutrino angular momentum loss, and the gravitational wave
signal due to rotation. We find that the mass shedding limit restricts the
initial angular momentum. Consequently, the final rotation frequency has to be
smaller than about 300 Hz for a PNS of about 1.6 solar masses whose EoS is
described by the GM3 mean-field model.
| [
{
"created": "Thu, 4 Jan 2018 13:52:20 GMT",
"version": "v1"
}
] | 2018-01-08 | [
[
"Camelio",
"Giovanni",
""
]
] | A proto-neutron star (PNS) is the first phase of life of a neutron star, and is likely to origin from a core-collapse supernova. After about 200 ms from core-collapse, the PNS evolution may be modeled as a sequence of quasi-stationary configurations. These configurations depend on the PNS thermodynamic profiles, whose evolution largely depends upon the neutrino diffusion. We developed a new PNS evolutionary code that solves by iteration the neutrino number and energy transport equations together with the relativistic stellar structure equations assuming spherical symmetry. The neutrino cross sections are determined consistently with the underlying equation of state (EoS). To include the EoSs in the evolution, we devised and tested a new fitting formula for the interacting part of the baryon free-energy, valid at finite temperature and arbitrary degeneracy. Using our code, we provide estimates for the neutrino signal in the Super-Kamiokande III detector and the frequencies of the gravitational waves due to stellar oscillations, for three stellar masses and three nucleonic EoSs. For the first time we evolve a PNS with a nuclear many-body theory EoS in a consistent way, that is, we take into account realistic nuclear interactions in the computation of the neutrino cross sections. By including rotation in an effective way, we have also determined the time variation of the rotation frequency due to PNS contraction and neutrino angular momentum loss, and the gravitational wave signal due to rotation. We find that the mass shedding limit restricts the initial angular momentum. Consequently, the final rotation frequency has to be smaller than about 300 Hz for a PNS of about 1.6 solar masses whose EoS is described by the GM3 mean-field model. |
1108.5618 | Drew Keppel | Kipp Cannon, Chad Hanna, Drew Keppel | Interpolating compact binary waveforms using the singular value
decomposition | 5 pages, 3 figures, presented at the joint 9th Edoardo Amaldi
Conference on Gravitational Waves and 2011 Numerical Relativity - Data
Analysis (NRDA) meeting | null | 10.1103/PhysRevD.85.081504 | LIGO-P1100101-v2 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Compact binary systems with total masses between tens and hundreds of solar
masses will produce gravitational waves during their merger phase that are
detectable by second-generation ground-based gravitational-wave detectors. In
order to model the gravitational waveform of the merger epoch of compact binary
coalescence, the full Einstein equations must be solved numerically for the
entire mass and spin parameter space. However, this is computationally
expensive. Several models have been proposed to interpolate the results of
numerical relativity simulations. In this paper we propose a numerical
interpolation scheme that stems from the singular value decomposition. This
algorithm shows promise in allowing one to construct arbitrary waveforms within
a certain parameter space given a sufficient density of numerical simulations
covering the same parameter space. We also investigate how similar approaches
could be used to interpolate waveforms in the context of parameter estimation.
| [
{
"created": "Mon, 29 Aug 2011 15:49:35 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Cannon",
"Kipp",
""
],
[
"Hanna",
"Chad",
""
],
[
"Keppel",
"Drew",
""
]
] | Compact binary systems with total masses between tens and hundreds of solar masses will produce gravitational waves during their merger phase that are detectable by second-generation ground-based gravitational-wave detectors. In order to model the gravitational waveform of the merger epoch of compact binary coalescence, the full Einstein equations must be solved numerically for the entire mass and spin parameter space. However, this is computationally expensive. Several models have been proposed to interpolate the results of numerical relativity simulations. In this paper we propose a numerical interpolation scheme that stems from the singular value decomposition. This algorithm shows promise in allowing one to construct arbitrary waveforms within a certain parameter space given a sufficient density of numerical simulations covering the same parameter space. We also investigate how similar approaches could be used to interpolate waveforms in the context of parameter estimation. |
gr-qc/0304049 | Hongya Liu | Lixin Xu, Hongya Liu, Beili Wang | On the Big Bounce Singularity of a Simple 5D Cosmological Model | Revtex, 10 pages, 2 figures, references added | Chin. Phys. Lett. 20 (2003) 995-998 | 10.1088/0256-307X/20/7/307 | null | gr-qc astro-ph | null | The big bounce singularity of a simple 5D cosmological model is studied.
Contrary to the standard big bang space-time singularity, this big bounce
singularity is found to be an event horizon at which the scale factor and the
mass density of the universe are finite, while the pressure undergoes a sudden
transition from negative infinity to positive infinity. By using coordinate
transformation it is also shown that before the bounce the universe contracts
deflationary, and the universe has been existed, according to the proper-time,
for an infinitely long time.
| [
{
"created": "Sun, 13 Apr 2003 11:52:42 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Jul 2003 02:18:17 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Xu",
"Lixin",
""
],
[
"Liu",
"Hongya",
""
],
[
"Wang",
"Beili",
""
]
] | The big bounce singularity of a simple 5D cosmological model is studied. Contrary to the standard big bang space-time singularity, this big bounce singularity is found to be an event horizon at which the scale factor and the mass density of the universe are finite, while the pressure undergoes a sudden transition from negative infinity to positive infinity. By using coordinate transformation it is also shown that before the bounce the universe contracts deflationary, and the universe has been existed, according to the proper-time, for an infinitely long time. |
gr-qc/0209024 | Vojtich Pravda | V. Pravda, A. Pravdova, A. Coley, R. Milson | All spacetimes with vanishing curvature invariants | 24 pages | Class.Quant.Grav.19:6213-6236,2002 | 10.1088/0264-9381/19/23/318 | null | gr-qc | null | All Lorentzian spacetimes with vanishing invariants constructed from the
Riemann tensor and its covariant derivatives are determined. A subclass of the
Kundt spacetimes results and we display the corresponding metrics in local
coordinates. Some potential applications of these spacetimes are discussed.
| [
{
"created": "Sat, 7 Sep 2002 19:46:43 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Pravda",
"V.",
""
],
[
"Pravdova",
"A.",
""
],
[
"Coley",
"A.",
""
],
[
"Milson",
"R.",
""
]
] | All Lorentzian spacetimes with vanishing invariants constructed from the Riemann tensor and its covariant derivatives are determined. A subclass of the Kundt spacetimes results and we display the corresponding metrics in local coordinates. Some potential applications of these spacetimes are discussed. |
2206.07031 | Thomas Osburn | Thomas Osburn and Nami Nishimura | New self-force method via elliptic partial differential equations for
Kerr inspiral models | Updated to match the published version | Physical Review D 106, 044056 (2022) | 10.1103/PhysRevD.106.044056 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a new method designed to avoid numerical challenges that have
impeded calculation of the Lorenz gauge self-force acting on a compact object
inspiraling into a Kerr black hole. This type of calculation is valuable in
creating waveform templates for extreme mass-ratio inspirals, which are an
important source of gravitational waves for the upcoming Laser Interferometer
Space Antenna mission. Prior hyperbolic partial differential equation (PDE)
formulations encountered numerical instabilities involving unchecked growth in
time; our new method is based on elliptic PDEs, which do not exhibit
instabilities of that kind. For proof of concept, we calculate the self-force
acting on a scalar charge in a circular orbit around a Kerr black hole. We
anticipate this method will subsequently facilitate calculation of first-order
Lorenz gauge Kerr metric perturbations and self-force, which could serve as a
foundation for second-order Kerr self-force investigations.
| [
{
"created": "Tue, 14 Jun 2022 17:52:17 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Sep 2022 20:27:15 GMT",
"version": "v2"
}
] | 2022-09-08 | [
[
"Osburn",
"Thomas",
""
],
[
"Nishimura",
"Nami",
""
]
] | We present a new method designed to avoid numerical challenges that have impeded calculation of the Lorenz gauge self-force acting on a compact object inspiraling into a Kerr black hole. This type of calculation is valuable in creating waveform templates for extreme mass-ratio inspirals, which are an important source of gravitational waves for the upcoming Laser Interferometer Space Antenna mission. Prior hyperbolic partial differential equation (PDE) formulations encountered numerical instabilities involving unchecked growth in time; our new method is based on elliptic PDEs, which do not exhibit instabilities of that kind. For proof of concept, we calculate the self-force acting on a scalar charge in a circular orbit around a Kerr black hole. We anticipate this method will subsequently facilitate calculation of first-order Lorenz gauge Kerr metric perturbations and self-force, which could serve as a foundation for second-order Kerr self-force investigations. |
1810.13119 | Sebastian Kish | Sebastian P. Kish, Timothy C. Ralph | Quantum Metrology in the Kerr Metric | 9 pages, 7 figures, closest to published version | Phys. Rev. D 99, 124015 (2019) | 10.1103/PhysRevD.99.124015 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A surprising feature of the Kerr metric is the anisotropy of the speed of
light. The angular momentum of a rotating massive object causes co- and
counter-propagating light paths to move at faster and slower velocities,
respectively as determined by a far-away clock. Based on this effect we derive
ultimate quantum limits for the measurement of the Kerr rotation parameter $a$
using a interferometric set up. As a possible implementation, we propose a
Mach-Zehnder interferometer to measure the "one-way height differential" time
effect. We isolate the effect by calibrating to a dark port and rotating the
interferometer such that only the direction dependent Kerr-metric induced phase
term remains. We transform to the Zero Angular Momentum Observer (ZAMO) flat
metric where the observer see $c=1$. We use this metric and the Lorentz
transformations to calculate the same Kerr phase shift. We then consider
non-stationary observers moving with the planet's rotation, and find a method
for cancelling the additional phase from the classical relative motion, thus
leaving only the curvature induced phase.
| [
{
"created": "Wed, 31 Oct 2018 06:26:12 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Jun 2019 03:01:11 GMT",
"version": "v2"
}
] | 2019-06-14 | [
[
"Kish",
"Sebastian P.",
""
],
[
"Ralph",
"Timothy C.",
""
]
] | A surprising feature of the Kerr metric is the anisotropy of the speed of light. The angular momentum of a rotating massive object causes co- and counter-propagating light paths to move at faster and slower velocities, respectively as determined by a far-away clock. Based on this effect we derive ultimate quantum limits for the measurement of the Kerr rotation parameter $a$ using a interferometric set up. As a possible implementation, we propose a Mach-Zehnder interferometer to measure the "one-way height differential" time effect. We isolate the effect by calibrating to a dark port and rotating the interferometer such that only the direction dependent Kerr-metric induced phase term remains. We transform to the Zero Angular Momentum Observer (ZAMO) flat metric where the observer see $c=1$. We use this metric and the Lorentz transformations to calculate the same Kerr phase shift. We then consider non-stationary observers moving with the planet's rotation, and find a method for cancelling the additional phase from the classical relative motion, thus leaving only the curvature induced phase. |
2401.05775 | Andronikos Paliathanasis | Andronikos Paliathanasis | Classical and Quantum solutions in Scalar field cosmology via the
Eisenhart lift and linearization | 18 pages, no figures | null | null | null | gr-qc hep-ph math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | This study introduces a novel approach for solving the cosmological field
equations within scalar field theory by employing the Eisenhart lift. The field
equations are reformulated as a system of geodesic equations for the Eisenhart
metric. In the case of an exponential potential, the Eisenhart metric is shown
to be conformally flat. By applying basic geometric principles, a new set of
dynamical variables is identified, allowing for the linearization of the field
equations and the derivation of classical cosmological solutions. However, the
quantization of the Eisenhart system reveals a distinct set of solutions for
the wavefunction, particularly in the presence of symmetry breaking at the
quantum level.
| [
{
"created": "Thu, 11 Jan 2024 09:27:23 GMT",
"version": "v1"
}
] | 2024-01-12 | [
[
"Paliathanasis",
"Andronikos",
""
]
] | This study introduces a novel approach for solving the cosmological field equations within scalar field theory by employing the Eisenhart lift. The field equations are reformulated as a system of geodesic equations for the Eisenhart metric. In the case of an exponential potential, the Eisenhart metric is shown to be conformally flat. By applying basic geometric principles, a new set of dynamical variables is identified, allowing for the linearization of the field equations and the derivation of classical cosmological solutions. However, the quantization of the Eisenhart system reveals a distinct set of solutions for the wavefunction, particularly in the presence of symmetry breaking at the quantum level. |
gr-qc/0401034 | Eric Black | Eric D. Black, Akira Villar, Kyle Barbary, Adam Bushmaker, Jay
Heefner, Seiji Kawamura, Fumiko Kawazoe, Luca Matone, Sharon Meidt, Shanti R.
Rao, Kevin Schulz, Michael Zhang, and Kenneth G. Libbrecht | Direct Observation of Broadband Coating Thermal Noise in a Suspended
Interferometer | Final version synchronized with publication in Phys. Lett. A | Phys.Lett. A328 (2004) 1-5 | 10.1016/j.physleta.2004.05.052 | null | gr-qc | null | We have directly observed broadband thermal noise in silica/tantala coatings
in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with
the prediction based on indirect, ring-down measurements of coating mechanical
loss, validating that method as a tool for the development of advanced
interferometric gravitational-wave detectors.
| [
{
"created": "Fri, 9 Jan 2004 22:11:00 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Apr 2005 21:38:28 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Black",
"Eric D.",
""
],
[
"Villar",
"Akira",
""
],
[
"Barbary",
"Kyle",
""
],
[
"Bushmaker",
"Adam",
""
],
[
"Heefner",
"Jay",
""
],
[
"Kawamura",
"Seiji",
""
],
[
"Kawazoe",
"Fumiko",
""
],
[
"Matone",
"Luca",
""
],
[
"Meidt",
"Sharon",
""
],
[
"Rao",
"Shanti R.",
""
],
[
"Schulz",
"Kevin",
""
],
[
"Zhang",
"Michael",
""
],
[
"Libbrecht",
"Kenneth G.",
""
]
] | We have directly observed broadband thermal noise in silica/tantala coatings in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with the prediction based on indirect, ring-down measurements of coating mechanical loss, validating that method as a tool for the development of advanced interferometric gravitational-wave detectors. |
1608.00559 | Sergio Ulhoa | S.C. Ulhoa, A.F. Santos, Faqir C. Khanna | Scattering of Fermions by Gravitons | null | Gen Relativ Gravit (2017) 49: 54 | 10.1007/s10714-017-2218-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The interaction between gravitons and fermions is investigated in the
teleparallel gravity. The scattering of fermions and gravitons in the weak
field approximation is analyzed. The transition amplitudes of
M$\varnothing$ller, Compton and new gravitational scattering are calculated.
| [
{
"created": "Fri, 29 Jul 2016 23:39:11 GMT",
"version": "v1"
}
] | 2017-11-30 | [
[
"Ulhoa",
"S. C.",
""
],
[
"Santos",
"A. F.",
""
],
[
"Khanna",
"Faqir C.",
""
]
] | The interaction between gravitons and fermions is investigated in the teleparallel gravity. The scattering of fermions and gravitons in the weak field approximation is analyzed. The transition amplitudes of M$\varnothing$ller, Compton and new gravitational scattering are calculated. |
2307.05011 | Tanmoy Paul | Shin'ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul, Soumitra SenGupta | Horizon entropy consistent with FLRW equations for general modified
theories of gravity and for all EoS of the matter field | PRD Accepted | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The question that continues to hinge the interrelation between cosmology and
thermodynamics is broadly described as -- what is the form of horizon entropy
that links the Friedmann equations for a "$general$" gravity theory with the
underlying thermodynamics of the apparent horizon? The answer to this question
was known only for Einstein's gravity and for $(n+1)$ dimensional Gauss-Bonnet
gravity theory, but not for a general modified theory of gravity (for instance,
the $F(R)$ gravity). In the present work, we take this issue and determine a
general form of entropy that connects the Friedmann equations for any gravity
theory with the apparent horizon thermodynamics given by $TdS = -dE + WdV$ (the
symbols have their usual meaning in the context of entropic cosmology and $W =
\left(\rho - p\right)/2$ is the work density of the matter fields represented
by $\rho$ and $p$ as the energy density and the pressure, respectively). Using
such generalized entropy, we find the respective entropies for several modified
theories of gravity (including the $F(R)$ gravity). Further, it turns out that
besides the above-mentioned question, the thermodynamic law $TdS = -dE + WdV$
itself has some serious difficulties for certain values of $\omega$ (the EoS of
matter field). Thus we propose a modified thermodynamic law of apparent
horizon, given by $TdS = -dE + \rho dV$, that is interestingly free from such
difficulties. The modified law proves to be valid for all EoS of the matter
field and thus is considered to be more general compared to the previous one
which, however, is a limiting case of the modified law for $p = -\rho$. Based
on such modified thermodynamics, we further determine a generalized entropy
that can provide the Friedmann equations of any general gravity theory for all
values of EoS of the matter field. The further implications are discussed.
| [
{
"created": "Tue, 11 Jul 2023 04:49:50 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Jan 2024 09:19:12 GMT",
"version": "v2"
}
] | 2024-01-30 | [
[
"Nojiri",
"Shin'ichi",
""
],
[
"Odintsov",
"Sergei D.",
""
],
[
"Paul",
"Tanmoy",
""
],
[
"SenGupta",
"Soumitra",
""
]
] | The question that continues to hinge the interrelation between cosmology and thermodynamics is broadly described as -- what is the form of horizon entropy that links the Friedmann equations for a "$general$" gravity theory with the underlying thermodynamics of the apparent horizon? The answer to this question was known only for Einstein's gravity and for $(n+1)$ dimensional Gauss-Bonnet gravity theory, but not for a general modified theory of gravity (for instance, the $F(R)$ gravity). In the present work, we take this issue and determine a general form of entropy that connects the Friedmann equations for any gravity theory with the apparent horizon thermodynamics given by $TdS = -dE + WdV$ (the symbols have their usual meaning in the context of entropic cosmology and $W = \left(\rho - p\right)/2$ is the work density of the matter fields represented by $\rho$ and $p$ as the energy density and the pressure, respectively). Using such generalized entropy, we find the respective entropies for several modified theories of gravity (including the $F(R)$ gravity). Further, it turns out that besides the above-mentioned question, the thermodynamic law $TdS = -dE + WdV$ itself has some serious difficulties for certain values of $\omega$ (the EoS of matter field). Thus we propose a modified thermodynamic law of apparent horizon, given by $TdS = -dE + \rho dV$, that is interestingly free from such difficulties. The modified law proves to be valid for all EoS of the matter field and thus is considered to be more general compared to the previous one which, however, is a limiting case of the modified law for $p = -\rho$. Based on such modified thermodynamics, we further determine a generalized entropy that can provide the Friedmann equations of any general gravity theory for all values of EoS of the matter field. The further implications are discussed. |
2310.05987 | Pardyumn Kumar Sahoo | Aaqid Bhat, Sanjay Mandal, P.K. Sahoo | Slow-roll inflation in $f(T,\mathcal{T})$ modified gravity | Chinese Physics C published version | Chinese Physics C volume 47 issue 12 (2023) 125104 | 10.1088/1674-1137/ad010f | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this article, we explore the concept of cosmological inflation within the
framework of the $f (T,\mathcal{T})$ theory of gravity, where $f$ is a general
function of the Torsion scalar $T$ and the trace, $\mathcal{T}$, of the
energy-momentum tensor. It is assumed that the conditions of slow-roll
inflation are applicable in$f (T,\mathcal{T})$ gravity. To determine different
observables related to inflation, such as the tensor-to-scalar ratio $r$,
scalar spectral index $n_s$, spectral index $ \alpha_s $, and tensor spectral
index $n_t$, the Hubble slow-roll parameters are utilized for a particular
model of $f (T,\mathcal{T})$. Lastly, an assessment has been carried out to
determine the feasibility of the models by conducting a numerical analysis of
the parameters. The findings indicate that it is feasible to achieve
compatibility with the observational measurements of slow-roll parameters by
utilizing different values of the free parameters.
| [
{
"created": "Sat, 7 Oct 2023 09:22:39 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Oct 2023 09:00:06 GMT",
"version": "v2"
}
] | 2023-11-14 | [
[
"Bhat",
"Aaqid",
""
],
[
"Mandal",
"Sanjay",
""
],
[
"Sahoo",
"P. K.",
""
]
] | In this article, we explore the concept of cosmological inflation within the framework of the $f (T,\mathcal{T})$ theory of gravity, where $f$ is a general function of the Torsion scalar $T$ and the trace, $\mathcal{T}$, of the energy-momentum tensor. It is assumed that the conditions of slow-roll inflation are applicable in$f (T,\mathcal{T})$ gravity. To determine different observables related to inflation, such as the tensor-to-scalar ratio $r$, scalar spectral index $n_s$, spectral index $ \alpha_s $, and tensor spectral index $n_t$, the Hubble slow-roll parameters are utilized for a particular model of $f (T,\mathcal{T})$. Lastly, an assessment has been carried out to determine the feasibility of the models by conducting a numerical analysis of the parameters. The findings indicate that it is feasible to achieve compatibility with the observational measurements of slow-roll parameters by utilizing different values of the free parameters. |
1607.07601 | Luc Blanchet | Tanguy Marchand, Luc Blanchet, Guillaume Faye | Gravitational-wave tail effects to quartic non-linear order | 32 pages, no figure, matches with published version | Classical and Quantum Gravity, 2016, 33, 244003 | 10.1088/0264-9381/33/24/244003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational-wave tails are due to the backscattering of linear waves onto
the space-time curvature generated by the total mass of the matter source. The
dominant tails correspond to quadratic non-linear interactions and arise at the
one-and-a-half post-Newtonian (1.5PN) order in the gravitational waveform. The
"tails-of-tails", which are cubic non-linear effects appearing at the 3PN order
in the waveform, are also known. We derive here higher non-linear tail effects,
namely those associated with quartic non-linear interactions or
"tails-of-tails-of-tails", which are shown to arise at the 4.5PN order. As an
application, we obtain at that order the complete coefficient in the total
gravitational-wave energy flux of compact binary systems moving on circular
orbits. Our result perfectly agrees with black-hole perturbation calculations
in the limit of extreme mass ratio of the two compact objects.
| [
{
"created": "Tue, 26 Jul 2016 09:19:09 GMT",
"version": "v1"
},
{
"created": "Mon, 28 Nov 2016 09:41:12 GMT",
"version": "v2"
}
] | 2016-12-07 | [
[
"Marchand",
"Tanguy",
""
],
[
"Blanchet",
"Luc",
""
],
[
"Faye",
"Guillaume",
""
]
] | Gravitational-wave tails are due to the backscattering of linear waves onto the space-time curvature generated by the total mass of the matter source. The dominant tails correspond to quadratic non-linear interactions and arise at the one-and-a-half post-Newtonian (1.5PN) order in the gravitational waveform. The "tails-of-tails", which are cubic non-linear effects appearing at the 3PN order in the waveform, are also known. We derive here higher non-linear tail effects, namely those associated with quartic non-linear interactions or "tails-of-tails-of-tails", which are shown to arise at the 4.5PN order. As an application, we obtain at that order the complete coefficient in the total gravitational-wave energy flux of compact binary systems moving on circular orbits. Our result perfectly agrees with black-hole perturbation calculations in the limit of extreme mass ratio of the two compact objects. |
1309.2454 | Jose Luis Hernandez-Pastora | J.L. Hernandez-Pastora | Linearized multipole solutions and their representation | 32 pages, 2 figures | 2013 Class. Quantum Grav. 30 175003 | 10.1088/0264-9381/30/17/175003 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The monopole solution of the Einstein vacuum field equations (Schwarzschild`s
solution) in Weyl coordinates involves a metric function that can be
interpreted as the gravitational potential of a bar of length $2m$ with
constant linear density. The question addressed in this work is whether similar
representations can be constructed for Weyl solutions other than the
spherically symmetric one.
A new family of static solutions of the axisymmetric vacuum field equations
generalizing the M-Q$^{(1)}$ solution is developed. These represent slight
deviations from spherical symmetry in terms of the relativistic multipole
moments (RMM) we wish the solution to contain. A Newtonian object referred to
as a dumbbell can be used to describe these solutions in a simple form by means
of the density of this object, since the physical properties of the
relativistic solution are characterized by its behaviour. The density profile
of the dumbbell, which is given in terms of the RMM of the solution, allows us
to distinguish general multipole Weyl solutions from the constant-density
Schwarzschild solution. The range of values of the multipole moments that
generate positive-definite density profiles are also calculated. The bounds on
the multipole moments that arise from this density condition are identical to
those required for a well-behaved infinite-redshift surface $g_{00}=0$.
| [
{
"created": "Tue, 10 Sep 2013 10:43:01 GMT",
"version": "v1"
}
] | 2013-09-11 | [
[
"Hernandez-Pastora",
"J. L.",
""
]
] | The monopole solution of the Einstein vacuum field equations (Schwarzschild`s solution) in Weyl coordinates involves a metric function that can be interpreted as the gravitational potential of a bar of length $2m$ with constant linear density. The question addressed in this work is whether similar representations can be constructed for Weyl solutions other than the spherically symmetric one. A new family of static solutions of the axisymmetric vacuum field equations generalizing the M-Q$^{(1)}$ solution is developed. These represent slight deviations from spherical symmetry in terms of the relativistic multipole moments (RMM) we wish the solution to contain. A Newtonian object referred to as a dumbbell can be used to describe these solutions in a simple form by means of the density of this object, since the physical properties of the relativistic solution are characterized by its behaviour. The density profile of the dumbbell, which is given in terms of the RMM of the solution, allows us to distinguish general multipole Weyl solutions from the constant-density Schwarzschild solution. The range of values of the multipole moments that generate positive-definite density profiles are also calculated. The bounds on the multipole moments that arise from this density condition are identical to those required for a well-behaved infinite-redshift surface $g_{00}=0$. |
1601.00868 | Antonin Coutant | Antonin Coutant, Florent Michel, Renaud Parentani | Dynamical instabilities and quasi-normal modes, a spectral analysis with
applications to black-hole physics | 31 pages, 13 figures. Small clarifications, title changed, matches
published version | Class. Quant. Grav. 33 (2016) 125032 | 10.1088/0264-9381/33/12/125032 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole dynamical instabilities have been mostly studied in specific
models. We here study the general properties of the complex-frequency modes
responsible for such instabilities, guided by the example of a charged scalar
field in an electrostatic potential. We show that these modes are square
integrable, have a vanishing conserved norm, and appear in mode doublets or
quartets. We also study how they appear in the spectrum and how their complex
frequencies subsequently evolve when varying some external parameter. When
working on an infinite domain, they appear from the reservoir of quasi-normal
modes obeying outgoing boundary conditions. This is illustrated by
generalizing, in a non-positive definite Krein space, a solvable model
(Friedrichs model) which originally describes the appearance of a resonance
when coupling an isolated system to a mode continuum. In a finite spatial
domain instead, they arise from the fusion of two real frequency modes with
opposite norms, through a process that closely resembles avoided crossing.
| [
{
"created": "Tue, 5 Jan 2016 15:41:00 GMT",
"version": "v1"
},
{
"created": "Fri, 1 Jul 2016 10:18:50 GMT",
"version": "v2"
}
] | 2016-07-04 | [
[
"Coutant",
"Antonin",
""
],
[
"Michel",
"Florent",
""
],
[
"Parentani",
"Renaud",
""
]
] | Black hole dynamical instabilities have been mostly studied in specific models. We here study the general properties of the complex-frequency modes responsible for such instabilities, guided by the example of a charged scalar field in an electrostatic potential. We show that these modes are square integrable, have a vanishing conserved norm, and appear in mode doublets or quartets. We also study how they appear in the spectrum and how their complex frequencies subsequently evolve when varying some external parameter. When working on an infinite domain, they appear from the reservoir of quasi-normal modes obeying outgoing boundary conditions. This is illustrated by generalizing, in a non-positive definite Krein space, a solvable model (Friedrichs model) which originally describes the appearance of a resonance when coupling an isolated system to a mode continuum. In a finite spatial domain instead, they arise from the fusion of two real frequency modes with opposite norms, through a process that closely resembles avoided crossing. |
gr-qc/0605007 | James Lindesay | James Lindesay | An Introduction of Multiple Scales in a Dynamical Cosmology | 8 pages, minor typo correction | null | null | null | gr-qc | null | The discovery of scale acceleration evidenced from supernovae luminosities
and spatial flatness of feature evolution in the cosmic microwave background
presents a challenge to the understanding of the evolution of cosmological
vacuum energy. Although some scenarios prefer a fixed cosmological constant
with dynamics governed in a Friedman-Robertson-Walker (FRW) geometry, an early
inflationary epoch remains a popular model for cosmology. It is therefore
advantageous to develop a metric framework that allows a transition from an
early inflationary period to a late stage dominated by dark energy. Such a
metric is here developed, and some properties of this metric are explored.
| [
{
"created": "Mon, 1 May 2006 14:14:15 GMT",
"version": "v1"
},
{
"created": "Tue, 9 May 2006 02:26:44 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Lindesay",
"James",
""
]
] | The discovery of scale acceleration evidenced from supernovae luminosities and spatial flatness of feature evolution in the cosmic microwave background presents a challenge to the understanding of the evolution of cosmological vacuum energy. Although some scenarios prefer a fixed cosmological constant with dynamics governed in a Friedman-Robertson-Walker (FRW) geometry, an early inflationary epoch remains a popular model for cosmology. It is therefore advantageous to develop a metric framework that allows a transition from an early inflationary period to a late stage dominated by dark energy. Such a metric is here developed, and some properties of this metric are explored. |
1904.08068 | Manuel Gonzalez-Espinoza | Manuel Gonzalez-Espinoza, Giovanni Otalora, Nelson Videla, Joel
Saavedra | Slow-roll inflation in generalized scalar-torsion gravity | Accepted for publication in JCAP | null | 10.1088/1475-7516/2019/08/029 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamics of inflation in a generalized scalar-torsion gravity
scenario by assuming a canonical scalar field non-minimally coupled to torsion
with a Galileon-type self-interaction. After obtaining the field equations for
a flat FRW background, we derive the second order action for both scalar and
tensor perturbations to compute the power spectra of primordial fluctuations.
As particular models, we studied at first, a power-law form of coupling
function $F(x)=1+\xi x^{2}/2$, with $x\equiv \phi/M_{pl}$, and a monomial
scalar field potential $V(x)=\lambda x^{n}/n$ which is ruled out at $2\sigma$
level by current observational data for $n\geq 2$. Under slow-roll
approximation we obtain analytical expressions for the background as well as
perturbative dynamics, and we show that the predictions of the model are
consistent with current Planck 2018 constraints on the spectral index $n_{s}$
and the tensor-to-scalar ratio $r$ through the $n_s-r$ plane. Accordingly, this
model is in agreement with current observational bounds only within the $95\%$
C.L. region in the case of chaotic quadratic inflation ($n=2$), whereas that
for the other monomial potentials such as $n=4/3$, $n=1$ and $n=2/3$, it is
found that they are even more favoured, overlapping their results with the
$68\%$ C.L. region from last Planck data. Secondly, we studied a model in which
the presence of both non-minimal coupling to gravity and the Galileon
non-linear self-interaction $\gamma (\partial \phi)^2 \Box{\phi}$ leads to a
suppression of the tensor-to-scalar ratio compared to those predicted in the
standard scenario, then predicting $0.024\lesssim r\lesssim 0.069$. This result
allows us to reconcile chaotic quadratic inflation with current Planck data up
to the $68\%$ C.L. region.
| [
{
"created": "Wed, 17 Apr 2019 03:38:26 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Aug 2019 01:41:55 GMT",
"version": "v2"
}
] | 2019-08-26 | [
[
"Gonzalez-Espinoza",
"Manuel",
""
],
[
"Otalora",
"Giovanni",
""
],
[
"Videla",
"Nelson",
""
],
[
"Saavedra",
"Joel",
""
]
] | We study the dynamics of inflation in a generalized scalar-torsion gravity scenario by assuming a canonical scalar field non-minimally coupled to torsion with a Galileon-type self-interaction. After obtaining the field equations for a flat FRW background, we derive the second order action for both scalar and tensor perturbations to compute the power spectra of primordial fluctuations. As particular models, we studied at first, a power-law form of coupling function $F(x)=1+\xi x^{2}/2$, with $x\equiv \phi/M_{pl}$, and a monomial scalar field potential $V(x)=\lambda x^{n}/n$ which is ruled out at $2\sigma$ level by current observational data for $n\geq 2$. Under slow-roll approximation we obtain analytical expressions for the background as well as perturbative dynamics, and we show that the predictions of the model are consistent with current Planck 2018 constraints on the spectral index $n_{s}$ and the tensor-to-scalar ratio $r$ through the $n_s-r$ plane. Accordingly, this model is in agreement with current observational bounds only within the $95\%$ C.L. region in the case of chaotic quadratic inflation ($n=2$), whereas that for the other monomial potentials such as $n=4/3$, $n=1$ and $n=2/3$, it is found that they are even more favoured, overlapping their results with the $68\%$ C.L. region from last Planck data. Secondly, we studied a model in which the presence of both non-minimal coupling to gravity and the Galileon non-linear self-interaction $\gamma (\partial \phi)^2 \Box{\phi}$ leads to a suppression of the tensor-to-scalar ratio compared to those predicted in the standard scenario, then predicting $0.024\lesssim r\lesssim 0.069$. This result allows us to reconcile chaotic quadratic inflation with current Planck data up to the $68\%$ C.L. region. |
2010.04047 | Simone Mastrogiovanni | S. Mastrogiovanni, L. Haegel, C. Karathanasis, I. Magana-Hernandez, D.
A. Steer | Gravitational wave friction in light of GW170817 and GW190521 | 17 pages, 6 figures, submitted to JCAP | null | 10.1088/1475-7516/2021/02/043 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use the gravitational wave (GW) events GW170817 and GW190521, together
with their proposed electromagnetic counterparts, to constrain cosmological
parameters and theories of gravity beyond General Relativity (GR). In
particular we consider models with a time-varying Planck mass, large
extra-dimensions, and a phenomenological parametrization covering several
beyond-GR theories. In all three cases, this introduces a friction term into
the GW propagation equation, effectively modifying the GW luminosity distance.
We set constraints on $\Lambda$CDM parameters and GR deviation parameters using
two sets of priors on the Hubble constant and matter energy density. With
priors set to the measured Planck's mission values, we find that with the
inclusion of GW190521, the two GR deviation parameters constraints improves by
a factor $\sim 10$, we report a number of spacetime dimensions compatible with
$4$ with an precision of $2.5\%$ (at 95\% CL) and an upper limit to the
variation of Netwon's constant at the epoch of GW170817 $<20\%$. With wide
priors on the Hubble constant and matter energy density, we show that it is
still possible to constrain the $\Lambda$CDM parameters and GR deviation
parameters conjointly from GW170817 and GW190521 obtaining constraints on GR
deviation parameters which are a factor $2-6$ worse than the results using
restricted priors on $\Lambda$CDM parameters.
| [
{
"created": "Thu, 8 Oct 2020 15:14:19 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Dec 2020 17:45:17 GMT",
"version": "v2"
}
] | 2021-03-03 | [
[
"Mastrogiovanni",
"S.",
""
],
[
"Haegel",
"L.",
""
],
[
"Karathanasis",
"C.",
""
],
[
"Magana-Hernandez",
"I.",
""
],
[
"Steer",
"D. A.",
""
]
] | We use the gravitational wave (GW) events GW170817 and GW190521, together with their proposed electromagnetic counterparts, to constrain cosmological parameters and theories of gravity beyond General Relativity (GR). In particular we consider models with a time-varying Planck mass, large extra-dimensions, and a phenomenological parametrization covering several beyond-GR theories. In all three cases, this introduces a friction term into the GW propagation equation, effectively modifying the GW luminosity distance. We set constraints on $\Lambda$CDM parameters and GR deviation parameters using two sets of priors on the Hubble constant and matter energy density. With priors set to the measured Planck's mission values, we find that with the inclusion of GW190521, the two GR deviation parameters constraints improves by a factor $\sim 10$, we report a number of spacetime dimensions compatible with $4$ with an precision of $2.5\%$ (at 95\% CL) and an upper limit to the variation of Netwon's constant at the epoch of GW170817 $<20\%$. With wide priors on the Hubble constant and matter energy density, we show that it is still possible to constrain the $\Lambda$CDM parameters and GR deviation parameters conjointly from GW170817 and GW190521 obtaining constraints on GR deviation parameters which are a factor $2-6$ worse than the results using restricted priors on $\Lambda$CDM parameters. |
1804.03371 | Titus K Mathew | Rajagopalan Nair K and Titus K. Mathew | A model of the late universe with viscous Zel'ldovich fluid and decaying
vacuum | 17 pages, 8 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Many have speculated about the presence of a stiff fluid in very early stage
of the universe. Such a stiff fluid was first introduced by Zel'dovich.
Recently the late acceleration of the universe was studied by taking bulk
viscous stiff fluid as the dominant cosmic component, but the age predicted by
such a model is less than the observed value. We consider a flat universe with
viscous stiff fluid and decaying vacuum energy as the cosmic components and
found that the model predicts a reasonable background evolution of the universe
with de Sitter epoch as end phase of expansion. More over the model also
predicts a reasonable value for the age of the present universe. We also
perform a dynamical system analysis of the model and found that the end de
Sitter phase predicted by the model is stable.
| [
{
"created": "Tue, 10 Apr 2018 07:04:05 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Apr 2018 16:09:16 GMT",
"version": "v2"
},
{
"created": "Wed, 25 Apr 2018 09:59:38 GMT",
"version": "v3"
},
{
"created": "Thu, 28 Jun 2018 08:08:51 GMT",
"version": "v4"
}
] | 2018-06-29 | [
[
"K",
"Rajagopalan Nair",
""
],
[
"Mathew",
"Titus K.",
""
]
] | Many have speculated about the presence of a stiff fluid in very early stage of the universe. Such a stiff fluid was first introduced by Zel'dovich. Recently the late acceleration of the universe was studied by taking bulk viscous stiff fluid as the dominant cosmic component, but the age predicted by such a model is less than the observed value. We consider a flat universe with viscous stiff fluid and decaying vacuum energy as the cosmic components and found that the model predicts a reasonable background evolution of the universe with de Sitter epoch as end phase of expansion. More over the model also predicts a reasonable value for the age of the present universe. We also perform a dynamical system analysis of the model and found that the end de Sitter phase predicted by the model is stable. |
1106.4695 | Luca Fabbri | Luca Fabbri | A Discussion on Dirac Field Theory, No-Go Theorems and Renormalizability | 10 pages | Int.J.Theor.Phys.52:634-643,2013 | 10.1007/s10773-012-1370-9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study Dirac field equations coupled to electrodynamics with metric and
torsion fields: we discuss how special spinorial solutions are incompatible
with torsion; eventually these results will be used to sketch a discussion on
the problem of renormalizability of point-like particles.
| [
{
"created": "Thu, 23 Jun 2011 12:22:56 GMT",
"version": "v1"
},
{
"created": "Sun, 14 Oct 2012 12:42:30 GMT",
"version": "v2"
}
] | 2013-04-11 | [
[
"Fabbri",
"Luca",
""
]
] | We study Dirac field equations coupled to electrodynamics with metric and torsion fields: we discuss how special spinorial solutions are incompatible with torsion; eventually these results will be used to sketch a discussion on the problem of renormalizability of point-like particles. |
gr-qc/0603034 | James Van Meter | Charles W. Misner, James R. van Meter, David R. Fiske | Excising das All: Evolving Maxwell waves beyond scri | 13 pages; incorporated material from gr-qc/0512167 | Phys.Rev.D74:064003,2006 | 10.1103/PhysRevD.74.064003 | null | gr-qc | null | We study the numerical propagation of waves through future null infinity in a
conformally compactified spacetime. We introduce an artificial cosmological
constant, which allows us some control over the causal structure near null
infinity. We exploit this freedom to ensure that all light cones are tilted
outward in a region near null infinity, which allows us to impose
excision-style boundary conditions in our finite difference code. In this
preliminary study we consider electromagnetic waves propagating in a static,
conformally compactified spacetime.
| [
{
"created": "Fri, 10 Mar 2006 02:00:44 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Sep 2006 07:05:50 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Misner",
"Charles W.",
""
],
[
"van Meter",
"James R.",
""
],
[
"Fiske",
"David R.",
""
]
] | We study the numerical propagation of waves through future null infinity in a conformally compactified spacetime. We introduce an artificial cosmological constant, which allows us some control over the causal structure near null infinity. We exploit this freedom to ensure that all light cones are tilted outward in a region near null infinity, which allows us to impose excision-style boundary conditions in our finite difference code. In this preliminary study we consider electromagnetic waves propagating in a static, conformally compactified spacetime. |
gr-qc/0312123 | Sergio M. C. V. Goncalves | Sergio M. C. V. Goncalves | Shear-free gravitational collapse is strongly censored | 6 pages, revtex4; accepted for publication in Phys. Rev. D Rapid Comm | Phys.Rev.D69:021502,2004 | 10.1103/PhysRevD.69.021502 | null | gr-qc | null | We consider spherically symmetric spacetimes with matter whose timelike flow
is assumed to be shear-free. A number of results on the formation and
visibility of spacetime singularities is proven, with the main one being that
shear-free collapse cannot admit locally naked singularities (which implies
absence of globally naked singularities). We conjecture that shear is a
necessary condition for the occurrence of locally naked singularities in
generic gravitational collapse.
| [
{
"created": "Tue, 30 Dec 2003 19:57:28 GMT",
"version": "v1"
}
] | 2010-05-12 | [
[
"Goncalves",
"Sergio M. C. V.",
""
]
] | We consider spherically symmetric spacetimes with matter whose timelike flow is assumed to be shear-free. A number of results on the formation and visibility of spacetime singularities is proven, with the main one being that shear-free collapse cannot admit locally naked singularities (which implies absence of globally naked singularities). We conjecture that shear is a necessary condition for the occurrence of locally naked singularities in generic gravitational collapse. |
2003.00286 | Zack Carson | Zack Carson and Kent Yagi | Probing Einstein-dilaton Gauss-Bonnet Gravity with the inspiral and
ringdown of gravitational waves | 12 pages, 4 figures; added a citation and DOI | Phys. Rev. D 101, 104030 (2020) | 10.1103/PhysRevD.101.104030 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves from extreme gravity events such as the coalescence of
two black holes in a binary system fill our observable universe, bearing with
them the underlying theory of gravity driving their process. One compelling
alternative theory of gravity -- known as Einstein-dilaton Gauss-Bonnet gravity
motivated by string theory -- describes the presence of an additional dilaton
scalar field coupled directly to higher orders of the curvature, effectively
describing a "fifth force" interaction and the emission of scalar dipole
radiation between two scalarized black holes. Most previous studies focused on
considering only the leading correction to the inspiral portion of the binary
black hole waveforms. In our recent paper, we carried out
inspiral-merger-ringdown consistency tests in this string-inspired gravity by
including corrections to both the inspiral and ringdown portions, as well as
those to the mass and spin of remnant black holes, valid to quadratic order in
spin. We here extend the analysis by directly computing bounds on the
theoretical coupling constant using the full inspiral-merger-ringdown waveform
rather than treating the inspiral and merger-ringdown portions separately. We
also consider the corrections valid to quartic order in spin to justify the
validity of black hole's slow-rotation approximation. We find the quasinormal
mode corrections to the waveform to be particularly important for high-mass
events such as GW170729, in which the dilaton fields' small-coupling
approximation fails without such effects included. We also show that future
space-based and multiband gravitational-wave observations have the potential to
go beyond existing bounds on the theory. The bounds presented here are
comparable to those found in via the inspiral-merger-ringdown consistency
tests.
| [
{
"created": "Sat, 29 Feb 2020 16:04:09 GMT",
"version": "v1"
},
{
"created": "Sat, 16 May 2020 02:55:12 GMT",
"version": "v2"
}
] | 2020-05-20 | [
[
"Carson",
"Zack",
""
],
[
"Yagi",
"Kent",
""
]
] | Gravitational waves from extreme gravity events such as the coalescence of two black holes in a binary system fill our observable universe, bearing with them the underlying theory of gravity driving their process. One compelling alternative theory of gravity -- known as Einstein-dilaton Gauss-Bonnet gravity motivated by string theory -- describes the presence of an additional dilaton scalar field coupled directly to higher orders of the curvature, effectively describing a "fifth force" interaction and the emission of scalar dipole radiation between two scalarized black holes. Most previous studies focused on considering only the leading correction to the inspiral portion of the binary black hole waveforms. In our recent paper, we carried out inspiral-merger-ringdown consistency tests in this string-inspired gravity by including corrections to both the inspiral and ringdown portions, as well as those to the mass and spin of remnant black holes, valid to quadratic order in spin. We here extend the analysis by directly computing bounds on the theoretical coupling constant using the full inspiral-merger-ringdown waveform rather than treating the inspiral and merger-ringdown portions separately. We also consider the corrections valid to quartic order in spin to justify the validity of black hole's slow-rotation approximation. We find the quasinormal mode corrections to the waveform to be particularly important for high-mass events such as GW170729, in which the dilaton fields' small-coupling approximation fails without such effects included. We also show that future space-based and multiband gravitational-wave observations have the potential to go beyond existing bounds on the theory. The bounds presented here are comparable to those found in via the inspiral-merger-ringdown consistency tests. |
2004.12566 | Yan Peng | Yan Peng | Spontaneous scalarization of Gauss-Bonnet black holes surrounded by
massive scalar fields | 8 pages, 1 figure | null | 10.1016/j.physletb.2020.135569 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For massless scalar fields, a relation $\Delta_{n}=\frac{\sqrt{3}}{2}\pi$ for
$n\rightarrow \infty$ was observed in the scalar-Gauss-Bonnet theory. In the
present paper, we extend the discussion by including a nonzero scalar field
mass. For massive scalar fields, we show that the relation
$\Delta_{n}=\frac{\sqrt{3}}{2}\pi$ for $n\rightarrow \infty$ still holds. We
demonstrate this relation with both analytical and numerical methods. The
analytical analysis implies that this relation may be a very universal
behavior.
| [
{
"created": "Mon, 27 Apr 2020 03:24:22 GMT",
"version": "v1"
}
] | 2020-06-24 | [
[
"Peng",
"Yan",
""
]
] | For massless scalar fields, a relation $\Delta_{n}=\frac{\sqrt{3}}{2}\pi$ for $n\rightarrow \infty$ was observed in the scalar-Gauss-Bonnet theory. In the present paper, we extend the discussion by including a nonzero scalar field mass. For massive scalar fields, we show that the relation $\Delta_{n}=\frac{\sqrt{3}}{2}\pi$ for $n\rightarrow \infty$ still holds. We demonstrate this relation with both analytical and numerical methods. The analytical analysis implies that this relation may be a very universal behavior. |
2311.13157 | RunDong Tang | RunDong Tang, Wen-Biao Han, XingYu Zhong, Ye Jiang, Ping Shen, Yu Wang | Prospect of detecting magnetic fields from strong-magnetized binary
neutron stars | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary neutron star mergers are unique sources of gravitational waves in
multi-messenger astronomy. The inspiral phase of binary neutron stars can emit
gravitational waves as chirp signals. The present waveform models of
gravitational wave only considered the gravitational interaction. In this
paper, we derive the waveform of the gravitational wave signal taking into
account the presence of magnetic fields. We found that the electromagnetic
interaction and radiation can introduce different frequency-dependent power
laws for both amplitude and frequency of the gravitational wave. We show from
the results of Fisher information matrix that the third-generation observation
may detect magnetic dipole moments if the magnetic field is around 10^17 G.
| [
{
"created": "Wed, 22 Nov 2023 04:42:59 GMT",
"version": "v1"
}
] | 2023-11-23 | [
[
"Tang",
"RunDong",
""
],
[
"Han",
"Wen-Biao",
""
],
[
"Zhong",
"XingYu",
""
],
[
"Jiang",
"Ye",
""
],
[
"Shen",
"Ping",
""
],
[
"Wang",
"Yu",
""
]
] | Binary neutron star mergers are unique sources of gravitational waves in multi-messenger astronomy. The inspiral phase of binary neutron stars can emit gravitational waves as chirp signals. The present waveform models of gravitational wave only considered the gravitational interaction. In this paper, we derive the waveform of the gravitational wave signal taking into account the presence of magnetic fields. We found that the electromagnetic interaction and radiation can introduce different frequency-dependent power laws for both amplitude and frequency of the gravitational wave. We show from the results of Fisher information matrix that the third-generation observation may detect magnetic dipole moments if the magnetic field is around 10^17 G. |
2303.03796 | Holger Frits Bech Nielsen | Holger Bech Nielsen and Masao Ninomiya | A new view on cosmology, with non-translational invariant Hamiltonian | This article is a contribution to the 25th Workshop in Bled on "What
comes beyond the Standard Models'' organized by Normankoc Borstnik , Maxim
khlopov , Astri Kleppe and Holger Bech Nielsen | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The idea of this contribution is to suggest a way to get rid of gravity as a
dynamical space time approximately in cosmology and thus be able to use
Hamiltonian formulation ignoring the gravitational degrees of freedom, treating
them just as background. Concretely we suggest to use a background De Sitter
spacetime and then instead of the usual choice of coordinates leading to a
picture in which the Universe Hubble expands, we propose to identify the time
translation in the new coordinate system with a Killing form transformation for
the De Sitter space time. This then leads to unwanted features like the
descripton being formally not translational invariant, but we have in mind just
to get in a simple way time translation and its associated Hamiltonian, and
shall then in word give some ideas of the from this point of view way of
looking at the usual cosmology.
| [
{
"created": "Tue, 7 Mar 2023 11:01:56 GMT",
"version": "v1"
}
] | 2023-03-08 | [
[
"Nielsen",
"Holger Bech",
""
],
[
"Ninomiya",
"Masao",
""
]
] | The idea of this contribution is to suggest a way to get rid of gravity as a dynamical space time approximately in cosmology and thus be able to use Hamiltonian formulation ignoring the gravitational degrees of freedom, treating them just as background. Concretely we suggest to use a background De Sitter spacetime and then instead of the usual choice of coordinates leading to a picture in which the Universe Hubble expands, we propose to identify the time translation in the new coordinate system with a Killing form transformation for the De Sitter space time. This then leads to unwanted features like the descripton being formally not translational invariant, but we have in mind just to get in a simple way time translation and its associated Hamiltonian, and shall then in word give some ideas of the from this point of view way of looking at the usual cosmology. |
gr-qc/0211057 | Tiberiu Harko | M. K. Mak, T. Harko | Quintessence and cosmic acceleration | 6 pages, 3 figures, to appear in Int. J. Mod. Phys. D | Int.J.Mod.Phys. D11 (2002) 1389-1397 | 10.1142/S0218271802002220 | null | gr-qc | null | A cosmological model with perfect fluid and self-interacting quintessence
field is considered in the framework of the spatially flat
Friedmann-Robertson-Walker (FRW) geometry. By assuming that all physical
quantities depend on the volume scale factor of the Universe, the general
solution of the gravitational field equations can be expressed in an exact
parametric form. The quintessence field is a free parameter. With an
appropriate choice of the scalar field a class of exact solutions is obtained,
with an exponential type scalar field potential fixed via the gravitational
field equations. The general physical behavior of the model is consistent with
the recent cosmological scenario favored by supernova Type Ia observations,
indicating an accelerated expansion of the Universe.
| [
{
"created": "Fri, 15 Nov 2002 08:17:30 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Mak",
"M. K.",
""
],
[
"Harko",
"T.",
""
]
] | A cosmological model with perfect fluid and self-interacting quintessence field is considered in the framework of the spatially flat Friedmann-Robertson-Walker (FRW) geometry. By assuming that all physical quantities depend on the volume scale factor of the Universe, the general solution of the gravitational field equations can be expressed in an exact parametric form. The quintessence field is a free parameter. With an appropriate choice of the scalar field a class of exact solutions is obtained, with an exponential type scalar field potential fixed via the gravitational field equations. The general physical behavior of the model is consistent with the recent cosmological scenario favored by supernova Type Ia observations, indicating an accelerated expansion of the Universe. |
1710.02724 | David Wallace | David Wallace | The case for black hole thermodynamics, Part I: phenomenological
thermodynamics | 36 pages. Minor revisions only | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I give a fairly systematic and thorough presentation of the case for
regarding black holes as thermodynamic systems in the fullest sense, aimed at
students and non-specialists and not presuming advanced knowledge of quantum
gravity. I pay particular attention to (i) the availability in classical black
hole thermodynamics of a well-defined notion of adiabatic intervention; (ii)
the power of the membrane paradigm to make black hole thermodynamics precise
and to extend it to local-equilibrium contexts; (iii) the central role of
Hawking radiation in permitting black holes to be in thermal contact with one
another; (iv) the wide range of routes by which Hawking radiation can be
derived and its back-reaction on the black hole calculated; (v) the
interpretation of Hawking radiation close to the black hole as a
gravitationally bound thermal atmosphere. In an appendix I discuss recent
criticisms of black hole thermodynamics by Dougherty and Callender. This paper
confines its attention to the thermodynamics of black holes; a sequel will
consider their statistical mechanics.
| [
{
"created": "Sat, 7 Oct 2017 19:17:10 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jun 2018 00:10:22 GMT",
"version": "v2"
}
] | 2018-06-18 | [
[
"Wallace",
"David",
""
]
] | I give a fairly systematic and thorough presentation of the case for regarding black holes as thermodynamic systems in the fullest sense, aimed at students and non-specialists and not presuming advanced knowledge of quantum gravity. I pay particular attention to (i) the availability in classical black hole thermodynamics of a well-defined notion of adiabatic intervention; (ii) the power of the membrane paradigm to make black hole thermodynamics precise and to extend it to local-equilibrium contexts; (iii) the central role of Hawking radiation in permitting black holes to be in thermal contact with one another; (iv) the wide range of routes by which Hawking radiation can be derived and its back-reaction on the black hole calculated; (v) the interpretation of Hawking radiation close to the black hole as a gravitationally bound thermal atmosphere. In an appendix I discuss recent criticisms of black hole thermodynamics by Dougherty and Callender. This paper confines its attention to the thermodynamics of black holes; a sequel will consider their statistical mechanics. |
1304.7612 | George Lukes Gerakopoulos | Georgios Lukes-Gerakopoulos and George Contopoulos | Mind the Resonances: Final stages of accretion into bumpy black holes | 10 pages, 7 figures, To appear in the proceedings of the conference,
NEB 15 - Recent Developments in Gravity - 20-23 June 2012, Chania, Greece | null | 10.1088/1742-6596/453/1/012005 | null | gr-qc astro-ph.SR nlin.CD | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we discuss a possible way of testing the Kerr black hole
hypothesis by taking advantage of phenomena correlated with chaotic motion in
the final stages of an accretion disk around a bumpy black hole. We anticipate
that these phenomena should have an imprint in the electromagnetic spectrum
coming from the accretion disk.
| [
{
"created": "Mon, 29 Apr 2013 10:19:07 GMT",
"version": "v1"
}
] | 2013-08-26 | [
[
"Lukes-Gerakopoulos",
"Georgios",
""
],
[
"Contopoulos",
"George",
""
]
] | In this article we discuss a possible way of testing the Kerr black hole hypothesis by taking advantage of phenomena correlated with chaotic motion in the final stages of an accretion disk around a bumpy black hole. We anticipate that these phenomena should have an imprint in the electromagnetic spectrum coming from the accretion disk. |
gr-qc/0210057 | Lluis Bel | Ll. Bel | A New Look to Massive Neutron Cores | 14 pages, Latex | null | null | null | gr-qc | null | We reconsider the problem of modelling static spherically symmetric perfect
fluid configurations with an equation of state from a point of view of that
requires the use of the concept of principal transform of a 3-dimensional
Riemannian metric. We discuss from this new point of view the meaning of those
familiar quantities that we call density, pressure and geometry in a
relativistic context. This is not simple semantics. To prove it we apply the
new ideas to recalculate the maximum mass that a massive neutron core can have.
This limit is found to be of the order of 3.8 $M_\odot$ substantially larger
than the Oppenheimer and Volkoff limit.
| [
{
"created": "Thu, 17 Oct 2002 16:26:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Bel",
"Ll.",
""
]
] | We reconsider the problem of modelling static spherically symmetric perfect fluid configurations with an equation of state from a point of view of that requires the use of the concept of principal transform of a 3-dimensional Riemannian metric. We discuss from this new point of view the meaning of those familiar quantities that we call density, pressure and geometry in a relativistic context. This is not simple semantics. To prove it we apply the new ideas to recalculate the maximum mass that a massive neutron core can have. This limit is found to be of the order of 3.8 $M_\odot$ substantially larger than the Oppenheimer and Volkoff limit. |
gr-qc/0410147 | Martin Bojowald | Martin Bojowald and Rafal Swiderski | Spherically Symmetric Quantum Horizons | 4 pages, RevTeX4 | Phys.Rev.D71:081501,2005 | 10.1103/PhysRevD.71.081501 | AEI-2004-099 | gr-qc | null | Isolated horizon conditions specialized to spherical symmetry can be imposed
directly at the quantum level. This answers several questions concerning
horizon degrees of freedom, which are seen to be related to orientation, and
its fluctuations at the kinematical as well as dynamical level. In particular,
in the absence of scalar or fermionic matter the horizon area is an approximate
quantum observable. Including different kinds of matter fields allows to probe
several aspects of the Hamiltonian constraint of quantum geometry that are
important in inhomogeneous situations.
| [
{
"created": "Fri, 29 Oct 2004 07:39:37 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Bojowald",
"Martin",
""
],
[
"Swiderski",
"Rafal",
""
]
] | Isolated horizon conditions specialized to spherical symmetry can be imposed directly at the quantum level. This answers several questions concerning horizon degrees of freedom, which are seen to be related to orientation, and its fluctuations at the kinematical as well as dynamical level. In particular, in the absence of scalar or fermionic matter the horizon area is an approximate quantum observable. Including different kinds of matter fields allows to probe several aspects of the Hamiltonian constraint of quantum geometry that are important in inhomogeneous situations. |
2201.11352 | Tao Zhu | Chao Zhang, Tao Zhu, Xiongjun Fang, and Anzhong Wang | Imprints of dark matter on gravitational ringing of supermassive black
holes | 15 pages, 6 figures, 4 tables. arXiv admin note: substantial text
overlap with arXiv:2111.04966; version appeared in Physics of the Dark
Universe | Physics of the Dark Universe 37 (2022) 10107 | 10.1016/j.dark.2022.101078 | null | gr-qc astro-ph.HE | http://creativecommons.org/publicdomain/zero/1.0/ | Gravitational waves emitted from the gravitational ringing of supermassive
black holes are important targets to test general relativity and probe the
matter environment surrounding such black holes. The main components of the
ringing waveform are black hole quasi-normal modes. In this paper, we study the
effects of the dark matter halos with three different density profiles on the
gravitational polar (even-parity) perturbations of a supermassive black hole.
For this purpose, we first consider modified Schwarzschild spacetime with three
different dark matter profiles and derive the equation of motion of the polar
perturbations of the supermassive black hole. It is shown that by ignoring the
dark matter perturbations, a Zerilli-like master equation with a modified
potential for the polar perturbation can be obtained explicitly. Then we
calculate the complex frequencies of the quasi-normal modes of the supermassive
black hole in the dark matter halos. The corresponding gravitational wave
spectra with the effects of the dark matter halos and their detectability have
also been discussed.
| [
{
"created": "Thu, 27 Jan 2022 07:17:28 GMT",
"version": "v1"
},
{
"created": "Sat, 2 Jul 2022 07:25:36 GMT",
"version": "v2"
}
] | 2022-07-05 | [
[
"Zhang",
"Chao",
""
],
[
"Zhu",
"Tao",
""
],
[
"Fang",
"Xiongjun",
""
],
[
"Wang",
"Anzhong",
""
]
] | Gravitational waves emitted from the gravitational ringing of supermassive black holes are important targets to test general relativity and probe the matter environment surrounding such black holes. The main components of the ringing waveform are black hole quasi-normal modes. In this paper, we study the effects of the dark matter halos with three different density profiles on the gravitational polar (even-parity) perturbations of a supermassive black hole. For this purpose, we first consider modified Schwarzschild spacetime with three different dark matter profiles and derive the equation of motion of the polar perturbations of the supermassive black hole. It is shown that by ignoring the dark matter perturbations, a Zerilli-like master equation with a modified potential for the polar perturbation can be obtained explicitly. Then we calculate the complex frequencies of the quasi-normal modes of the supermassive black hole in the dark matter halos. The corresponding gravitational wave spectra with the effects of the dark matter halos and their detectability have also been discussed. |
gr-qc/9907054 | Emulsion-Lab | S.Q. Wu and X. Cai | Maxwell-Boltzmann, Bose-Einstein, Fermi-Dirac statistical entropies in a
D-dimensional stationary axisymmetry space-time | 22 pages, no figure, in revtex (12pt), submitted to Phys. Rev. D | null | null | null | gr-qc | null | Statistical entropies of a general relativistic ideal gas obeying
Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac statistics are calculated in a
general axisymmetry space-time of arbitrary dimension. This general formation
can be used to discuss the entropy of a quantum field not only in the flat
space-time but also in a curved space-time. It can also be used to compare the
entropies in different dimensional space-times. Analytical expressions for the
thermodynamic potentials are presented, and their behaviors in the high or low
temperature approximation are discussed. The entropy of a quantum field is
shown to be proportional to the volume of optical space or that of the dragged
optical space only in the high temperature approximation or in the zero mass
case. In the case of a black hole, the entropy of a quantum field at the
Hartle-Hawking temperature is proportional to the horizon "area" if and only if
the horizon is located at the light velocity surface.
| [
{
"created": "Fri, 16 Jul 1999 10:17:32 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wu",
"S. Q.",
""
],
[
"Cai",
"X.",
""
]
] | Statistical entropies of a general relativistic ideal gas obeying Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac statistics are calculated in a general axisymmetry space-time of arbitrary dimension. This general formation can be used to discuss the entropy of a quantum field not only in the flat space-time but also in a curved space-time. It can also be used to compare the entropies in different dimensional space-times. Analytical expressions for the thermodynamic potentials are presented, and their behaviors in the high or low temperature approximation are discussed. The entropy of a quantum field is shown to be proportional to the volume of optical space or that of the dragged optical space only in the high temperature approximation or in the zero mass case. In the case of a black hole, the entropy of a quantum field at the Hartle-Hawking temperature is proportional to the horizon "area" if and only if the horizon is located at the light velocity surface. |
1408.2691 | Sean Gryb B | Sean Gryb, Karim Thebault | Time Remains | 30 pages, 1 figure. Version accepted for publication in the British
Journal for the Philosophy of Science | null | 10.1093/bjps/axv009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | On one popular view, the general covariance of gravity implies that change is
relational in a strong sense, such that all it is for a physical degree of
freedom to change is for it to vary with regard to a second physical degree of
freedom. At a quantum level, this view of "change as relative variation" leads
to a "fundamentally timeless" formalism for quantum gravity. Here, we will show
how one may avoid this acute `problem of time'. Under our view, duration is
still regarded as relative, but temporal succession is taken to be absolute.
Following our approach, which is presented in more formal terms in
arXiv:1303.7139, it is possible to conceive of a genuinely dynamical theory of
quantum gravity within which time, in a substantive sense, remains.
| [
{
"created": "Tue, 12 Aug 2014 11:09:00 GMT",
"version": "v1"
}
] | 2018-01-18 | [
[
"Gryb",
"Sean",
""
],
[
"Thebault",
"Karim",
""
]
] | On one popular view, the general covariance of gravity implies that change is relational in a strong sense, such that all it is for a physical degree of freedom to change is for it to vary with regard to a second physical degree of freedom. At a quantum level, this view of "change as relative variation" leads to a "fundamentally timeless" formalism for quantum gravity. Here, we will show how one may avoid this acute `problem of time'. Under our view, duration is still regarded as relative, but temporal succession is taken to be absolute. Following our approach, which is presented in more formal terms in arXiv:1303.7139, it is possible to conceive of a genuinely dynamical theory of quantum gravity within which time, in a substantive sense, remains. |
1805.08825 | Timothy Walton | Robin W. Tucker and Timothy J. Walton | Chirality in Gravitational and Electromagnetic Interactions with Matter | 17 pages, 5 figures, Proceedings for 'Geometric Foundations of
Gravity', Tartu, 2017 | null | 10.1142/S0219887818400042 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been suggested that single and double jets observed emanating from
certain astrophysical objects may have a purely gravitational origin. We
discuss new classes of pulsed gravitational wave solutions to the equation for
perturbations of Ricci-flat spacetimes around Minkowski metrics, as models for
the genesis of such phenomena. We discuss how these solutions are motivated by
the analytic structure of spatially compact finite energy pulse solutions of
the source-free Maxwell equations generated from complex chiral eigenmodes of a
chirality operator. Complex gravitational pulse solutions to the linearised
source-free Einstein equations are classified in terms of their chirality and
generate a family of non-stationary real spacetime metrics. Particular members
of these families are used as backgrounds in analysing time-like solutions to
the geodesic equation for test particles. They are found numerically to exhibit
both single and double jet-like features with dimensionless aspect ratios
suggesting that it may be profitable to include such backgrounds in simulations
of astrophysical jet dynamics from rotating accretion discs involving
electromagnetic fields.
| [
{
"created": "Tue, 22 May 2018 19:32:09 GMT",
"version": "v1"
}
] | 2018-05-24 | [
[
"Tucker",
"Robin W.",
""
],
[
"Walton",
"Timothy J.",
""
]
] | It has been suggested that single and double jets observed emanating from certain astrophysical objects may have a purely gravitational origin. We discuss new classes of pulsed gravitational wave solutions to the equation for perturbations of Ricci-flat spacetimes around Minkowski metrics, as models for the genesis of such phenomena. We discuss how these solutions are motivated by the analytic structure of spatially compact finite energy pulse solutions of the source-free Maxwell equations generated from complex chiral eigenmodes of a chirality operator. Complex gravitational pulse solutions to the linearised source-free Einstein equations are classified in terms of their chirality and generate a family of non-stationary real spacetime metrics. Particular members of these families are used as backgrounds in analysing time-like solutions to the geodesic equation for test particles. They are found numerically to exhibit both single and double jet-like features with dimensionless aspect ratios suggesting that it may be profitable to include such backgrounds in simulations of astrophysical jet dynamics from rotating accretion discs involving electromagnetic fields. |
2008.07963 | Elena Medina | Elena Medina and Luis Mart\'inez Alonso | Kinetic dominance and psi series in the Hamilton-Jacobi formulation of
inflaton models | 30 pages, 9 figures | Phys. Rev. D 102, 103517 (2020) | 10.1103/PhysRevD.102.103517 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Single-field inflaton models in the kinetic dominance period admit formal
solutions given by generalized asymptotic expansions called psi series. We
present a method for computing psi series for the Hubble parameter as a
function of the inflaton field in the Hamilton-Jacobi formulation of inflaton
models. Similar psi series for the scale factor, the conformal time and the
Hubble radius are also derived. They are applied to determine the value of the
inflaton field when the inflation period starts and to estimate the
contribution of the kinetic dominance period to calculate the duration of
inflation. These psi series are also used to obtain explicit two-term truncated
psi series near the singularity for the potentials of the Mukhanov-Sasaki
equation for curvature and tensor perturbations. The method is illustrated with
wide families of inflaton models determined by potential functions combining
polynomial and exponential functions as well as with generalized Starobinsky
models.
| [
{
"created": "Tue, 18 Aug 2020 14:50:02 GMT",
"version": "v1"
},
{
"created": "Sun, 15 Nov 2020 17:45:32 GMT",
"version": "v2"
}
] | 2020-11-18 | [
[
"Medina",
"Elena",
""
],
[
"Alonso",
"Luis Martínez",
""
]
] | Single-field inflaton models in the kinetic dominance period admit formal solutions given by generalized asymptotic expansions called psi series. We present a method for computing psi series for the Hubble parameter as a function of the inflaton field in the Hamilton-Jacobi formulation of inflaton models. Similar psi series for the scale factor, the conformal time and the Hubble radius are also derived. They are applied to determine the value of the inflaton field when the inflation period starts and to estimate the contribution of the kinetic dominance period to calculate the duration of inflation. These psi series are also used to obtain explicit two-term truncated psi series near the singularity for the potentials of the Mukhanov-Sasaki equation for curvature and tensor perturbations. The method is illustrated with wide families of inflaton models determined by potential functions combining polynomial and exponential functions as well as with generalized Starobinsky models. |
2109.12752 | Viqar Husain | Viqar Husain, Suprit Singh | Quantum backreaction on a classical universe | 7 pages, 2 figures | Phys. Rev. D 104, 124048 (2021) | 10.1103/PhysRevD.104.124048 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We study a first-order formulation for the coupled evolution of a quantum
scalar field and a classical Friedmann universe. The model is defined by a
state dependent hamiltonian constraint and the time dependent Schr\"odinger
equation for the scalar field. We solve the resulting non-linear equations
numerically for initial data consisting of a Gaussian scalar field state and
gravity phase space variables. This gives a self-consistent semiclassical
evolution that includes non-perturbative ``backreaction" due to particle
production. We compare the results with the evolution of a quantum scalar field
on a fixed background, and find that the backreaction modifies both particle
production and cosmological expansion, and that these effects remain bounded.
| [
{
"created": "Mon, 27 Sep 2021 01:30:34 GMT",
"version": "v1"
}
] | 2021-12-20 | [
[
"Husain",
"Viqar",
""
],
[
"Singh",
"Suprit",
""
]
] | We study a first-order formulation for the coupled evolution of a quantum scalar field and a classical Friedmann universe. The model is defined by a state dependent hamiltonian constraint and the time dependent Schr\"odinger equation for the scalar field. We solve the resulting non-linear equations numerically for initial data consisting of a Gaussian scalar field state and gravity phase space variables. This gives a self-consistent semiclassical evolution that includes non-perturbative ``backreaction" due to particle production. We compare the results with the evolution of a quantum scalar field on a fixed background, and find that the backreaction modifies both particle production and cosmological expansion, and that these effects remain bounded. |
1411.0325 | Zacharias Roupas | Zacharias Roupas | Corrigendum to "Thermodynamical instabilities of perfect fluid spheres
in General Relativity" | 4 pages | Class. Quantum Grav. 32 119501 (2015) | 10.1088/0264-9381/32/11/119501 | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In [1], the thermal equilibrium of static, spherically symmetric perfect
fluids in General Relativity was studied. I would like to elaborate three
points relevant to the results of [1]. The first point is only a clarification,
summarized in theorem 1 below, of results that appear in [1]. The following two
points correct the error in [1], stating that the condition for thermodynamic
stability, found in [1], is referring to the microcanonical ensemble, while it
was referring to the canonical one. In theorems 2 and 3, specific cases for
which equivalence of dynamical and thermodynamic stability holds are specified.
| [
{
"created": "Sun, 2 Nov 2014 21:45:27 GMT",
"version": "v1"
},
{
"created": "Mon, 11 May 2015 16:18:43 GMT",
"version": "v2"
}
] | 2015-05-12 | [
[
"Roupas",
"Zacharias",
""
]
] | In [1], the thermal equilibrium of static, spherically symmetric perfect fluids in General Relativity was studied. I would like to elaborate three points relevant to the results of [1]. The first point is only a clarification, summarized in theorem 1 below, of results that appear in [1]. The following two points correct the error in [1], stating that the condition for thermodynamic stability, found in [1], is referring to the microcanonical ensemble, while it was referring to the canonical one. In theorems 2 and 3, specific cases for which equivalence of dynamical and thermodynamic stability holds are specified. |
2302.01173 | Gabriele Barca | Gabriele Barca, Giovanni Montani, Alessandro Melchiorri | Emergent Universe Model from Modified Heisenberg Algebra | 12 pages, 6 figures. New upload to match published version | Phys. Rev. D 108, 063505 (2023) | 10.1103/PhysRevD.108.063505 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide an Emergent Universe picture in which the fine-tuning on the
initial conditions is replaced by cut-off physics, implemented on a
semiclassical level when referred to the Universe dynamics and on a purely
quantum level for the quantum fluctuations of the inflaton field. The adopted
cut-off physics is inspired by Polymer Quantum Mechanics but expanded in the
limit of a small lattice step. On a quasi-classical level, this results in
modified Poisson Brackets for the Hamiltonian Universe dynamics similar to a
Generalized Uncertainty Principle algebra. The resulting Universe is indeed
asymptotically Einstein-static, emerging from a finite volume configuration in
the distant past and then properly reconnecting with the most relevant Universe
phases. The calculation of the modifications of the primordial inflaton
spectrum is then performed by treating new physics as a small correction on the
standard Hamiltonian of each Fourier mode of the field. The merit of this study
is to provide a new paradigm for a non-singular Emergent Universe, which is
associated with a precise fingerprint on the temperature distribution of the
microwave background, in principle observable by future experiments.
| [
{
"created": "Thu, 2 Feb 2023 15:50:14 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Sep 2023 10:51:18 GMT",
"version": "v2"
}
] | 2023-09-11 | [
[
"Barca",
"Gabriele",
""
],
[
"Montani",
"Giovanni",
""
],
[
"Melchiorri",
"Alessandro",
""
]
] | We provide an Emergent Universe picture in which the fine-tuning on the initial conditions is replaced by cut-off physics, implemented on a semiclassical level when referred to the Universe dynamics and on a purely quantum level for the quantum fluctuations of the inflaton field. The adopted cut-off physics is inspired by Polymer Quantum Mechanics but expanded in the limit of a small lattice step. On a quasi-classical level, this results in modified Poisson Brackets for the Hamiltonian Universe dynamics similar to a Generalized Uncertainty Principle algebra. The resulting Universe is indeed asymptotically Einstein-static, emerging from a finite volume configuration in the distant past and then properly reconnecting with the most relevant Universe phases. The calculation of the modifications of the primordial inflaton spectrum is then performed by treating new physics as a small correction on the standard Hamiltonian of each Fourier mode of the field. The merit of this study is to provide a new paradigm for a non-singular Emergent Universe, which is associated with a precise fingerprint on the temperature distribution of the microwave background, in principle observable by future experiments. |
1308.6587 | Vitor Cardoso | Vitor Cardoso, Isabella P. Carucci, Paolo Pani, Thomas P. Sotiriou | Black holes with surrounding matter in scalar-tensor theories | 5 pages. Published version. arXiv admin note: substantial text
overlap with arXiv:1305.6936 | Phys.Rev.Lett. 111, 111101 (2013) | 10.1103/PhysRevLett.111.111101 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We uncover two mechanisms that can render Kerr black holes unstable in
scalar-tensor gravity, both associated to the presence of matter in the
vicinity of the black hole and the fact that this introduces an effective mass
for the scalar. Our results highlight the importance of understanding the
structure of spacetime in realistic, astrophysical black holes in scalar-tensor
theories.
| [
{
"created": "Thu, 29 Aug 2013 20:00:23 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Oct 2013 10:24:08 GMT",
"version": "v2"
}
] | 2015-06-17 | [
[
"Cardoso",
"Vitor",
""
],
[
"Carucci",
"Isabella P.",
""
],
[
"Pani",
"Paolo",
""
],
[
"Sotiriou",
"Thomas P.",
""
]
] | We uncover two mechanisms that can render Kerr black holes unstable in scalar-tensor gravity, both associated to the presence of matter in the vicinity of the black hole and the fact that this introduces an effective mass for the scalar. Our results highlight the importance of understanding the structure of spacetime in realistic, astrophysical black holes in scalar-tensor theories. |
1111.6248 | Jose Luis Jaramillo | Mar\'ia E. Gabach Cl\'ement, Jos\'e Luis Jaramillo | Black hole Area-Angular momentum-Charge inequality in dynamical
non-vacuum spacetimes | 4 pages, no figures | null | 10.1103/PhysRevD.86.064021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the area-angular momentum-charge inequality (A/(4\pi))^2 \geq
(2J)^2 + (Q_E^2 + Q_M^2)^2 holds for apparent horizons of electrically and
magnetically charged rotating black holes in generic dynamical and non-vacuum
spacetimes. More specifically, this quasi-local inequality applies to axially
symmetric closed outermost stably marginally (outer) trapped surfaces, embedded
in non-necessarily axisymmetric black hole spacetimes with non-negative
cosmological constant and matter content satisfying the dominant energy
condition.
| [
{
"created": "Sun, 27 Nov 2011 11:28:53 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Clément",
"María E. Gabach",
""
],
[
"Jaramillo",
"José Luis",
""
]
] | We show that the area-angular momentum-charge inequality (A/(4\pi))^2 \geq (2J)^2 + (Q_E^2 + Q_M^2)^2 holds for apparent horizons of electrically and magnetically charged rotating black holes in generic dynamical and non-vacuum spacetimes. More specifically, this quasi-local inequality applies to axially symmetric closed outermost stably marginally (outer) trapped surfaces, embedded in non-necessarily axisymmetric black hole spacetimes with non-negative cosmological constant and matter content satisfying the dominant energy condition. |
2004.09651 | Igor Khavkine | Igor Khavkine | Explicit Triangular Decoupling of the Separated Lichnerowicz Tensor Wave
Equation on Schwarzschild into Scalar Regge-Wheeler Equations | v2: 57 pages, presentation rearranged and remarks added for clarity;
published version | SIGMA 18 (2022), 011, 57 pages | 10.3842/SIGMA.2022.011 | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | We consider the vector and the Lichnerowicz wave equations on the
Schwarzschild spacetime, which correspond to the Maxwell and linearized
Einstein equations in harmonic gauges (or, respectively, in Lorenz and de
Donder gauges). After a complete separation of variables, the radial mode
equations form complicated systems of coupled linear ODEs. We outline a precise
abstract strategy to decouple these systems into sparse triangular form, where
the diagonal blocks consist of spin-$s$ scalar Regge-Wheeler equations (for
spins $s=0,1,2$). Building on the example of the vector wave equation, which we
have treated previously, we complete a successful implementation of our
strategy for the Lichnerowicz wave equation. Our results go a step further than
previous more ad-hoc attempts in the literature by presenting a full and
maximally simplified final triangular form. These results have important
applications to the quantum field theory of and the classical stability
analysis of electromagnetic and gravitational perturbations of the
Schwarzschild black hole in harmonic gauges.
| [
{
"created": "Mon, 20 Apr 2020 21:41:22 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Feb 2022 12:47:46 GMT",
"version": "v2"
}
] | 2022-02-07 | [
[
"Khavkine",
"Igor",
""
]
] | We consider the vector and the Lichnerowicz wave equations on the Schwarzschild spacetime, which correspond to the Maxwell and linearized Einstein equations in harmonic gauges (or, respectively, in Lorenz and de Donder gauges). After a complete separation of variables, the radial mode equations form complicated systems of coupled linear ODEs. We outline a precise abstract strategy to decouple these systems into sparse triangular form, where the diagonal blocks consist of spin-$s$ scalar Regge-Wheeler equations (for spins $s=0,1,2$). Building on the example of the vector wave equation, which we have treated previously, we complete a successful implementation of our strategy for the Lichnerowicz wave equation. Our results go a step further than previous more ad-hoc attempts in the literature by presenting a full and maximally simplified final triangular form. These results have important applications to the quantum field theory of and the classical stability analysis of electromagnetic and gravitational perturbations of the Schwarzschild black hole in harmonic gauges. |
2107.07679 | Giovanni Otalora | Mat\'ias L\'opez, Giovanni Otalora, Nelson Videla | Chaotic Inflation and Reheating in Generalized Scalar-Tensor Gravity | 26 pages, 8 figures, 2 tables. Accepted version for publication in
JCAP | JCAP10(2021)021 | 10.1088/1475-7516/2021/10/021 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present work, we study slow-roll inflation in scalar-tensor gravity
theories in the presence of both the non-minimal coupling between the scalar
field and curvature, and the Galileon self-interaction of the scalar field.
Furthermore, we give predictions for the duration of reheating as well as for
the reheating temperature after inflation. After working out the expressions
for the power spectra of scalar and tensor perturbations in the case of a
general non-minimal coupling function that depends solely on the scalar field
and a general scalar potential, we focus on the special cases of the power-law
coupling function and chaotic quadratic inflation. Thus, under the slow-roll
approximation we confront the predictions of the model with the current PLANCK
constraints on the spectral index $n_s$ and the tensor-to-scalar ratio $r$
using the $n_{s}-r$ plane. We found that the combination of the non-minimal
coupling and Galileon self-interaction effects allows us to obtain better
results for $r$ than in the case in which each effect is considered separately.
Particularly, we obtained that the predictions of the model are in agreement
with the current observational bounds on $n_{s}$ and $r$ within the $95 \%$ C.L
region and also slightly inside the $68 \%$ C.L region. Also, we investigate
the oscillatory regime after the end of inflation by solving the full
background equations, and then we determine the upper bound for the Galileon
and non-minimal coupling parameters under the condition that the scalar field
oscillates coherently during reheating. Finally, after approximating reheating
by a constant equation of state, we derive the relations between the reheating
duration, the temperature at the end of reheating, its equation of state, and
the number of $e$-folds of inflation and then we relate them all to the
inflationary observables.
| [
{
"created": "Fri, 16 Jul 2021 02:55:00 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Sep 2021 18:38:29 GMT",
"version": "v2"
}
] | 2021-11-11 | [
[
"López",
"Matías",
""
],
[
"Otalora",
"Giovanni",
""
],
[
"Videla",
"Nelson",
""
]
] | In the present work, we study slow-roll inflation in scalar-tensor gravity theories in the presence of both the non-minimal coupling between the scalar field and curvature, and the Galileon self-interaction of the scalar field. Furthermore, we give predictions for the duration of reheating as well as for the reheating temperature after inflation. After working out the expressions for the power spectra of scalar and tensor perturbations in the case of a general non-minimal coupling function that depends solely on the scalar field and a general scalar potential, we focus on the special cases of the power-law coupling function and chaotic quadratic inflation. Thus, under the slow-roll approximation we confront the predictions of the model with the current PLANCK constraints on the spectral index $n_s$ and the tensor-to-scalar ratio $r$ using the $n_{s}-r$ plane. We found that the combination of the non-minimal coupling and Galileon self-interaction effects allows us to obtain better results for $r$ than in the case in which each effect is considered separately. Particularly, we obtained that the predictions of the model are in agreement with the current observational bounds on $n_{s}$ and $r$ within the $95 \%$ C.L region and also slightly inside the $68 \%$ C.L region. Also, we investigate the oscillatory regime after the end of inflation by solving the full background equations, and then we determine the upper bound for the Galileon and non-minimal coupling parameters under the condition that the scalar field oscillates coherently during reheating. Finally, after approximating reheating by a constant equation of state, we derive the relations between the reheating duration, the temperature at the end of reheating, its equation of state, and the number of $e$-folds of inflation and then we relate them all to the inflationary observables. |
gr-qc/0006067 | Alejandro Corichi | A. Corichi and J.M. Reyes | A Gaussian Weave for Kinematical Loop Quantum Gravity | 15 pages, 3 figures, Revtex file. Comments added and references
updated. Final version to appear in IJMP-D | Int.J.Mod.Phys. D10 (2001) 325-338 | 10.1142/S0218271801000846 | ICN-UNAM-00/09 | gr-qc hep-th | null | Remarkable efforts in the study of the semi-classical regime of kinematical
loop quantum gravity are currently underway. In this note, we construct a
``quasi-coherent'' weave state using Gaussian factors. In a similar fashion to
some other proposals, this state is peaked in both the connection and the spin
network basis. However, the state constructed here has the novel feature that,
in the spin network basis, the main contribution for this state is given by the
fundamental representation, independently of the value of the parameter that
regulates the Gaussian width.
| [
{
"created": "Tue, 20 Jun 2000 01:28:32 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Aug 2000 14:48:36 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Corichi",
"A.",
""
],
[
"Reyes",
"J. M.",
""
]
] | Remarkable efforts in the study of the semi-classical regime of kinematical loop quantum gravity are currently underway. In this note, we construct a ``quasi-coherent'' weave state using Gaussian factors. In a similar fashion to some other proposals, this state is peaked in both the connection and the spin network basis. However, the state constructed here has the novel feature that, in the spin network basis, the main contribution for this state is given by the fundamental representation, independently of the value of the parameter that regulates the Gaussian width. |
gr-qc/9710081 | M. Rainer | M. Rainer | The role of dilations in diffeomorphism covariant algebraic quantum
field theory | 11 pages, LaTeX, typos corrected | Int.J.Theor.Phys.39:259-275,2000 | 10.1023/A:1003676023771 | Uni-P-Math/15-10-97 | gr-qc | null | The quantum analogue of general relativistic geometry should be implementable
on smooth manifolds without an a priori metric structure, the kinematical
covariance group acting by diffeomorphisms.
Here I approach quantum gravity (QG) in the view of constructive, algebraic
quantum field theory (QFT). Comparing QG with usual QFT, the algebraic approach
clarifies analogies and peculiarities. As usual, an isotonic net of *-algebras
is taken to encode the quantum field operators. For QG, the kinematical
covariance group acts via diffeomorphisms on the open sets of the manifold, and
via algebraic isomorphisms on the algebras. In general, the algebra of
observables is covariant only under a (dynamical) subgroup of the general
diffeomorphism group.
After an algebraic implementation of the dynamical subgroup of dilations,
small and large scale cutoffs may be introduced algebraically. So the usual a
priori conflict of cutoffs with general covariance is avoided. Even more, these
cutoffs provide a natural local cobordism for topological quantum field theory.
A new commutant duality between the minimal and maximal algebra allows to
extract the modular structure from the net of algebras. The outer modular
isomorphisms are then again related to dilations, which (under certain
conditions) may provide a notion of time.
| [
{
"created": "Wed, 15 Oct 1997 21:46:16 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Nov 1997 11:46:44 GMT",
"version": "v2"
},
{
"created": "Fri, 2 Apr 1999 06:14:04 GMT",
"version": "v3"
}
] | 2011-04-20 | [
[
"Rainer",
"M.",
""
]
] | The quantum analogue of general relativistic geometry should be implementable on smooth manifolds without an a priori metric structure, the kinematical covariance group acting by diffeomorphisms. Here I approach quantum gravity (QG) in the view of constructive, algebraic quantum field theory (QFT). Comparing QG with usual QFT, the algebraic approach clarifies analogies and peculiarities. As usual, an isotonic net of *-algebras is taken to encode the quantum field operators. For QG, the kinematical covariance group acts via diffeomorphisms on the open sets of the manifold, and via algebraic isomorphisms on the algebras. In general, the algebra of observables is covariant only under a (dynamical) subgroup of the general diffeomorphism group. After an algebraic implementation of the dynamical subgroup of dilations, small and large scale cutoffs may be introduced algebraically. So the usual a priori conflict of cutoffs with general covariance is avoided. Even more, these cutoffs provide a natural local cobordism for topological quantum field theory. A new commutant duality between the minimal and maximal algebra allows to extract the modular structure from the net of algebras. The outer modular isomorphisms are then again related to dilations, which (under certain conditions) may provide a notion of time. |
1506.07759 | Giuseppe Sellaroli | Florian Girelli, Giuseppe Sellaroli | 3d Lorentzian loop quantum gravity and the spinor approach | Fixed typos. 28 pages, 3 figures. To appear in Phys. Rev. D | Phys. Rev. D 92, 124035 (2015) | 10.1103/PhysRevD.92.124035 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the generalization of the "spinor approach" to the Lorentzian
case, in the context of 3d loop quantum gravity with cosmological constant
$\Lambda=0$. The key technical tool that allows this generalization is the
recoupling theory between unitary infinite-dimensional representations and
non-unitary finite-dimensional ones, obtained in the process of generalizing
the Wigner-Eckart theorem to SU(1,1). We use SU(1,1) tensor operators to build
observables and a solvable quantum Hamiltonian constraint, analogue of the one
introduced by V. Bonzom and his collaborators in the Euclidean case (with both
$\Lambda=0$ and $\Lambda\neq0$). We show that the Lorentzian Ponzano-Regge
amplitude is solution of the quantum Hamiltonian constraint by recovering the
Biedenharn-Elliott relation (generalized to the case where unitary and
non-unitary SU(1,1) representations are coupled to each other). Our formalism
is sufficiently general that both the Lorentzian and the Euclidean case can be
recovered (with $\Lambda=0$).
| [
{
"created": "Thu, 25 Jun 2015 14:07:42 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Nov 2015 21:44:07 GMT",
"version": "v2"
}
] | 2015-12-23 | [
[
"Girelli",
"Florian",
""
],
[
"Sellaroli",
"Giuseppe",
""
]
] | We consider the generalization of the "spinor approach" to the Lorentzian case, in the context of 3d loop quantum gravity with cosmological constant $\Lambda=0$. The key technical tool that allows this generalization is the recoupling theory between unitary infinite-dimensional representations and non-unitary finite-dimensional ones, obtained in the process of generalizing the Wigner-Eckart theorem to SU(1,1). We use SU(1,1) tensor operators to build observables and a solvable quantum Hamiltonian constraint, analogue of the one introduced by V. Bonzom and his collaborators in the Euclidean case (with both $\Lambda=0$ and $\Lambda\neq0$). We show that the Lorentzian Ponzano-Regge amplitude is solution of the quantum Hamiltonian constraint by recovering the Biedenharn-Elliott relation (generalized to the case where unitary and non-unitary SU(1,1) representations are coupled to each other). Our formalism is sufficiently general that both the Lorentzian and the Euclidean case can be recovered (with $\Lambda=0$). |
gr-qc/0501031 | Carsten Gundlach | David Garfinkle and Carsten Gundlach | Well-posedness of the scale-invariant tetrad formulation of the vacuum
Einstein equations | Added section on the well-posedness of the constraint evolution
system | Class.Quant.Grav. 22 (2005) 2679-2686 | 10.1088/0264-9381/22/13/011 | null | gr-qc | null | We show that with a small modification, the formulation of the Einstein
equations of Uggla et al, which uses tetrad variables normalised by the
expansion, is a mixed symmetric hyperbolic/parabolic system. Well-posedness of
the Cauchy problem follows from a standard theorem.
| [
{
"created": "Mon, 10 Jan 2005 14:17:55 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Jun 2005 17:34:52 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Garfinkle",
"David",
""
],
[
"Gundlach",
"Carsten",
""
]
] | We show that with a small modification, the formulation of the Einstein equations of Uggla et al, which uses tetrad variables normalised by the expansion, is a mixed symmetric hyperbolic/parabolic system. Well-posedness of the Cauchy problem follows from a standard theorem. |
2407.04735 | S. Davood Sadatian | S. Davood Sadatian, Amir Sabouri, Zahra Davari | Loop Quantum Gravity and CMB Anisotropy | 15 pages, 3 figures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Recent satellite observations have revealed significant anisotropy in the
cosmic microwave background (CMB) radiation, a phenomenon that had previously
been detected but received limited attention due to its subtlety. With the
advent of more precise measurements from satellites, the extent of this
anisotropy has become increasingly apparent. This paper examines the CMB
radiation by reviewing past research on the causes of CMB anisotropy and
presents a new model to explain the observed temperature anisotropy and the
anisotropy in the correlation function between temperature and E-mode
polarization in the CMB radiation. The proposed model is based on a
modified-generalized Compton scattering approach incorporating Loop Quantum
Gravity (LQG). We begin by describing the generalized Compton scattering and
then discuss the CMB radiation in the context of processes occurring at the
last scattering surface. Our findings are derived from the latest observational
data from the Planck satellite (2018). In our model, besides the parameters
available in the Planck data for the standard model ($\Lambda$CDM), we
introduce two novel parameters: $\delta_{L}$, the density of cosmic electrons,
and $M^2$, a parameter related to the modified-generalized Compton scattering
effects. The results indicate that, based on the 2018 Planck data, small values
were obtained for $\delta_{L}$ and $M^{2}$, $\delta_{L}=1.63\pm0.08(10^{-13})$
and $M^2=2.28\pm0.34(10^{-4})$), showing no significant deviation from the
standard model. Moreover, increasing the values of $\delta_{L}$ and $M^{2}$
leads to an increase in the range of fluctuations in the CMB temperature
anisotropy power spectrum and the correlation function between temperature and
E-mode polarization for multipoles $l<500$ until the first peak.
| [
{
"created": "Mon, 1 Jul 2024 10:34:49 GMT",
"version": "v1"
}
] | 2024-07-09 | [
[
"Sadatian",
"S. Davood",
""
],
[
"Sabouri",
"Amir",
""
],
[
"Davari",
"Zahra",
""
]
] | Recent satellite observations have revealed significant anisotropy in the cosmic microwave background (CMB) radiation, a phenomenon that had previously been detected but received limited attention due to its subtlety. With the advent of more precise measurements from satellites, the extent of this anisotropy has become increasingly apparent. This paper examines the CMB radiation by reviewing past research on the causes of CMB anisotropy and presents a new model to explain the observed temperature anisotropy and the anisotropy in the correlation function between temperature and E-mode polarization in the CMB radiation. The proposed model is based on a modified-generalized Compton scattering approach incorporating Loop Quantum Gravity (LQG). We begin by describing the generalized Compton scattering and then discuss the CMB radiation in the context of processes occurring at the last scattering surface. Our findings are derived from the latest observational data from the Planck satellite (2018). In our model, besides the parameters available in the Planck data for the standard model ($\Lambda$CDM), we introduce two novel parameters: $\delta_{L}$, the density of cosmic electrons, and $M^2$, a parameter related to the modified-generalized Compton scattering effects. The results indicate that, based on the 2018 Planck data, small values were obtained for $\delta_{L}$ and $M^{2}$, $\delta_{L}=1.63\pm0.08(10^{-13})$ and $M^2=2.28\pm0.34(10^{-4})$), showing no significant deviation from the standard model. Moreover, increasing the values of $\delta_{L}$ and $M^{2}$ leads to an increase in the range of fluctuations in the CMB temperature anisotropy power spectrum and the correlation function between temperature and E-mode polarization for multipoles $l<500$ until the first peak. |
gr-qc/9607055 | Jack Gegenberg | J. Gegenberg, G. Kunstatter, and T. Strobl | Statistical Mechanical Entropy of Two-Dimensional Black Holes | Important acknowledgments added; typos corrected. Uses sprocl.sty | null | null | null | gr-qc hep-th | null | We calculate the statistical mechanical entropy associated with boundary
terms in the two-dimensional Euclidean black holes in deSitter gravity.
| [
{
"created": "Tue, 23 Jul 1996 15:58:58 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Mar 1997 14:36:43 GMT",
"version": "v2"
}
] | 2008-02-03 | [
[
"Gegenberg",
"J.",
""
],
[
"Kunstatter",
"G.",
""
],
[
"Strobl",
"T.",
""
]
] | We calculate the statistical mechanical entropy associated with boundary terms in the two-dimensional Euclidean black holes in deSitter gravity. |
2209.04783 | Marko Vojinovic | Nikola Paunkovic and Marko Vojinovic | Operational verification of the existence of a spacetime manifold | v2: various text improvements, several typos fixed. 14+4 pages, 7
figures | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We argue that there exists an operational way to establish the objective
reality of the notions of space and time. Specifically, we propose a
theory-independent protocol for a gedanken-experiment, whose outcome is a
signal establishing the observability of the spacetime manifold, without a
priori assuming its existence. The experimental signal contains the information
about the dimension and the topology of spacetime (with the currently
achievable precision), and establishes its manifold structure, while respecting
its underlying diffeomorphism symmetry. We also introduce and discuss
appropriate criteria for the concept of emergence of spacetime, which any
tentative theoretical model of physics must satisfy in order to claim that
spacetime does emerge from some more fundamental concepts.
| [
{
"created": "Sun, 11 Sep 2022 04:29:25 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Feb 2024 17:17:41 GMT",
"version": "v2"
}
] | 2024-02-12 | [
[
"Paunkovic",
"Nikola",
""
],
[
"Vojinovic",
"Marko",
""
]
] | We argue that there exists an operational way to establish the objective reality of the notions of space and time. Specifically, we propose a theory-independent protocol for a gedanken-experiment, whose outcome is a signal establishing the observability of the spacetime manifold, without a priori assuming its existence. The experimental signal contains the information about the dimension and the topology of spacetime (with the currently achievable precision), and establishes its manifold structure, while respecting its underlying diffeomorphism symmetry. We also introduce and discuss appropriate criteria for the concept of emergence of spacetime, which any tentative theoretical model of physics must satisfy in order to claim that spacetime does emerge from some more fundamental concepts. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.